I have also confirmed this.

Problem: pdftops is failing when trying to fax pdf's from hplip 2.8.2.

Steps:
Fully updated system
Install latest hplip 2.8.2 from source
--although hplip isn't causing this problem, so the hplip version wont matter
Attempt to send a fax using hp-sendfax
--you will likely get an error that rendering fail.
Check cups (locahost:631/printers) notice error: "/usr/lib/cups/filter/pdftops failed" for the fax queue.

Expected:  pdftops should convert the pdf to ps with no errors.

I believe this problem is because pdftops no longer supports the -cfg option, and it is still getting passed the option from cupsys (I assume cupsys anyway.)

Verified pdftops file.pdf file.ps works correctly.  pdftops is correctly converting pdf files to ps.

From the cups log:

E [21/Feb/2008:15:41:30 -0800] [Job 7] pdftops-options: -cfg /etc/cups/pdftops.conf
D [21/Feb/2008:15:41:30 -0800] Discarding unused printer-state-changed event...
D [21/Feb/2008:15:41:30 -0800] [Job 7] pdftops version 3.00
D [21/Feb/2008:15:41:30 -0800] [Job 7] Copyright 1996-2004 Glyph & Cog, LLC
D [21/Feb/2008:15:41:30 -0800] [Job 7] Usage: pdftops [options] <PDF-file> [<PS-file>]
D [21/Feb/2008:15:41:30 -0800] [Job 7] -f <int>            : first page to print
D [21/Feb/2008:15:41:30 -0800] [Job 7] -l <int>            : last page to print
D [21/Feb/2008:15:41:30 -0800] [Job 7] -level1             : generate Level 1 PostScript
D [21/Feb/2008:15:41:30 -0800] [Job 7] -level1sep          : generate Level 1 separable PostScript
D [21/Feb/2008:15:41:30 -0800] [Job 7] -level2             : generate Level 2 PostScript
D [21/Feb/2008:15:41:30 -0800] [Job 7] -level2sep          : generate Level 2 separable PostScript
D [21/Feb/2008:15:41:30 -0800] [Job 7] -level3             : generate Level 3 PostScript
D [21/Feb/2008:15:41:30 -0800] [Job 7] -level3sep          : generate Level 3 separable PostScript
D [21/Feb/2008:15:41:30 -0800] [Job 7] -eps                : generate Encapsulated PostScript (EPS)
D [21/Feb/2008:15:41:30 -0800] [Job 7] -form               : generate a PostScript form
D [21/Feb/2008:15:41:30 -0800] [Job 7] -opi                : generate OPI comments
D [21/Feb/2008:15:41:30 -0800] [Job 7] -noembt1            : don't embed Type 1 fonts
D [21/Feb/2008:15:41:30 -0800] [Job 7] -noembtt            : don't embed TrueType fonts
D [21/Feb/2008:15:41:30 -0800] [Job 7] -noembcidps         : don't embed CID PostScript fonts
D [21/Feb/2008:15:41:30 -0800] [Job 7] -noembcidtt         : don't embed CID TrueType fonts
D [21/Feb/2008:15:41:30 -0800] [Job 7] -preload            : preload images and forms
D [21/Feb/2008:15:41:30 -0800] [Job 7] -paper <string>     : paper size (letter, legal, A4, A3, match)
D [21/Feb/2008:15:41:30 -0800] [Job 7] -paperw <int>       : paper width, in points
D [21/Feb/2008:15:41:30 -0800] [Job 7] -paperh <int>       : paper height, in points
D [21/Feb/2008:15:41:30 -0800] [Job 7] -nocrop             : don't crop pages to CropBox
D [21/Feb/2008:15:41:30 -0800] [Job 7] -expand             : expand pages smaller than the paper size
D [21/Feb/2008:15:41:30 -0800] [Job 7] -noshrink           : don't shrink pages larger than the paper size
D [21/Feb/2008:15:41:30 -0800] [Job 7] -nocenter           : don't center pages smaller than the paper size
D [21/Feb/2008:15:41:30 -0800] [Job 7] -duplex             : enable duplex printing
D [21/Feb/2008:15:41:30 -0800] [Job 7] -opw <string>       : owner password (for encrypted files)
D [21/Feb/2008:15:41:30 -0800] [Job 7] -upw <string>       : user password (for encrypted files)
D [21/Feb/2008:15:41:30 -0800] [Job 7] -q                  : don't print any messages or errors
D [21/Feb/2008:15:41:30 -0800] [Job 7] -v                  : print copyright and version info
D [21/Feb/2008:15:41:30 -0800] [Job 7] -h                  : print usage information
D [21/Feb/2008:15:41:30 -0800] [Job 7] -help               : print usage information
D [21/Feb/2008:15:41:30 -0800] [Job 7] --help              : print usage information
D [21/Feb/2008:15:41:30 -0800] [Job 7] -?                  : print usage information
E [21/Feb/2008:15:41:30 -0800] [Job 7] /usr/bin/pdftops exited with  exit code 1

As you can see something is passing the -cfg option:
E [21/Feb/2008:15:41:30 -0800] [Job 7] pdftops-options: -cfg /etc/cups/pdftops.conf

Verifed that the /etc/cups/pdftops.conf file location is valid:
aaron@localhost:/usr/lib/cups/filter$ ls -l /etc/cups/pdftops.conf
-rw-r--r-- 1 root root 1573 2008-01-29 12:54 /etc/cups/pdftops.conf

Verified in the /usr/lib/cups/filter/pdftops script that the correct pdftops file (/usr/bin/pdftops) is being executed. (below)

...from /usr/lib/cups/filter/pdftops:..
# Site specific parameters - modify as needed
# ----------------------------------------------------------------------------------
$pdftops_path = "/usr/bin/pdftops";             # path to the xpdf utility
$acroread_path = "/usr/bin/acroread";           # path to Adobe Reader
$default_app = 'use-pdftops';                   # the default if both are configured
# ------------------

man pdftops indicates that the -cfg option is valid:

       -cfg config-file
              Read config-file in place of ~/.xpdfrc or the system-wide config file.

Current version of pdftops installed:

aaron@localhost:/usr/lib/cups/filter$ pdftops -v
pdftops version 3.00
Copyright 1996-2004 Glyph & Cog, LLC

The pdftops --help does not indicate that the -cfg option is valid:

aaron@localhost:/usr/lib/cups/filter$ pdftops --help
pdftops version 3.00
Copyright 1996-2004 Glyph & Cog, LLC
Usage: pdftops [options] <PDF-file> [<PS-file>]
  -f <int>            : first page to print
  -l <int>            : last page to print
  -level1             : generate Level 1 PostScript
  -level1sep          : generate Level 1 separable PostScript
  -level2             : generate Level 2 PostScript
  -level2sep          : generate Level 2 separable PostScript
  -level3             : generate Level 3 PostScript
  -level3sep          : generate Level 3 separable PostScript
  -eps                : generate Encapsulated PostScript (EPS)
  -form               : generate a PostScript form
  -opi                : generate OPI comments
  -noembt1            : don't embed Type 1 fonts
  -noembtt            : don't embed TrueType fonts
  -noembcidps         : don't embed CID PostScript fonts
  -noembcidtt         : don't embed CID TrueType fonts
  -preload            : preload images and forms
  -paper <string>     : paper size (letter, legal, A4, A3, match)
  -paperw <int>       : paper width, in points
  -paperh <int>       : paper height, in points
  -nocrop             : don't crop pages to CropBox
  -expand             : expand pages smaller than the paper size
  -noshrink           : don't shrink pages larger than the paper size
  -nocenter           : don't center pages smaller than the paper size
  -duplex             : enable duplex printing
  -opw <string>       : owner password (for encrypted files)
  -upw <string>       : user password (for encrypted files)
  -q                  : don't print any messages or errors
  -v                  : print copyright and version info
  -h                  : print usage information
  -help               : print usage information
  --help              : print usage information
  -?                  : print usage information

Perhaps the -cfg options was valid in a previous version of pdftops but is no longer valid?

Printerbuginfo script:

ProblemType: printingbuginfo v2.0: printingbug (https://wiki.ubuntu.com/PrintingBugInfoScript)
CupsConfiguredDevices:
 device for PDF: cups-pdf:/
 device for Photosmart_C7200: hp:/usb/Photosmart_C7200_series?serial=MY736140B204YG
 device for Photosmart_C7200_fax: hpfax:/usb/Photosmart_C7200_series?serial=MY736140B204YG
 device for Photosmart_C7200_series: hp:/usb/Photosmart_C7200_series?serial=MY736140B204YG
 device for Photosmart_C7200_series_fax: hpfax:/usb/Photosmart_C7200_series?serial=MY736140B204YG
CupsConfiguredPPDs:
 PDF: Generic PDF file generator
 Photosmart_C7200: HP PhotoSmart 7260 Foomatic/hpijs, hpijs 2.8.2
 Photosmart_C7200_fax: HP Fax
 Photosmart_C7200_series: HP PhotoSmart C7100 Foomatic/hpijs, hpijs 2.8.2
 Photosmart_C7200_series_fax: HP Fax
Date: Thu Feb 21 16:09:52 2008
DesktopEnvironment: GNOME
DistroRelease: Ubuntu 8.04
EtcPapersize: letter
InstalledPrintingPackages:
 ii  cupsys                   1.3.5-1ubuntu3           Common UNIX Printing System(tm) - server
 ii  cupsys-driver-gutenprint 5.0.2-2ubuntu1           printer drivers for CUPS
 ii  foo2zjs                  20071205-0ubuntu1        Support for printing to ZjStream-based printers
 ii  foomatic-db              20080211-0ubuntu1        OpenPrinting printer support - database
 ii  foomatic-db-engine       3.0.2-20070719-0ubuntu4  OpenPrinting printer support - programs
 ii  foomatic-filters         3.0.2-20071204-0ubuntu1  OpenPrinting printer support - filters
 ii  ghostscript              8.61.dfsg.1-1ubuntu2     The GPL Ghostscript PostScript/PDF interpreter
 ii  libgnomeprint2.2-0       2.18.4-1~hardy1          The GNOME 2.2 print architecture - runtime files
 ii  min12xxw                 0.0.9-1build1            Printer driver for KonicaMinolta PagePro 1[234]xxW
 ii  openprinting-ppds        20080211-0ubuntu1        OpenPrinting printer support - PostScript PPD files
 ii  pnm2ppa                  1.12-16                  PPM to PPA converter
 ii  pxljr                    1.1-0ubuntu1             Driver for HP's Color LaserJet 35xx/36xx color laser printers
 ii  splix                    1.1.1-0ubuntu1           Driver for Samsung's SPL2 (bw) and SPLc (color) laser printers
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8, LC_PAPER=en_US.UTF-8
Uname: Linux dhcp59049.vcd.hp.com 2.6.24-8-generic #1 SMP Thu Feb 14 20:13:27 UTC 2008 x86_64 GNU/Linux