OK, here's some better testing from me...

I used a different Ubuntu 9.04 32-bit system where I hadn't tested this before.  It has this sort of USB interface:

  00:1d.7 USB Controller: Intel Corporation 82801G (ICH7 Family) USB2 EHCI Controller (rev 01)

The system is running up-to-date Jaunty with this kernel:

  Linux spot 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:57:59 UTC 2009 i686 GNU/Linux

My Sansa e260 has an extra 8GB Micro SDHC card.  It is running the old bootloader that boots into the original Sansa firmware when the device is off and then the USB is plugged in.  It is also running Rockbox r20338-090317 - yes, that's from March...  but it works...  ;-)

For each state of my Ubuntu system (see below) I did 2 tests:

1. From e260 off: With the e260's power off, I plugged in the USB  cable and let
   the device boot into the original Sansa firmware.  The expected result is that
   the filesystem on the built-in 4GB flash storage is mounted.

2. From e260 on: With the e260's power on, running Rockbox, I plugged in the
   USB cable and Rockbox detected the USB connection.  The expected result is
   that the filesystems on both the built-in 4GB flash storage and the additional
   8GB Micro SDHC card are separately mounted.  That is, I should see 2 mounted
   filesystems.

Tests:

1. Standard Jaunty system with no PPA packages.

   Both tests fail.  I don't see any log messages after:

     usb-storage: waiting for device to settle before scanning

2. Jaunty system with my PPA packages, before reboot.

   Both tests pass - both filesystems are mounted.

3. Jaunty system with my PPA packages, after reboot.

   Both tests pass - both filesystems are mounted.

Notes:

* I'm running 32-bit Jaunty.

* I have not attempted to apply any other fixes for this bug including
   configuration hacks involving modifications to or removal of:

     /usr/share/hal/fdi/preprobe/10osvendor/20-libgphoto2.fdi

Logs for a successful test "from e260 on" look like this:

[  135.287119] usb-storage: waiting for device to settle before scanning
[  140.286255] usb-storage: device scan complete
[  140.288490] scsi 4:0:0:0: Direct-Access     Rockbox  Internal Storage 0.00 PQ: 0 ANSI: 4
[  140.291855] scsi 4:0:0:1: Direct-Access     Rockbox  SD Card Slot     0.00 PQ: 0 ANSI: 4
[  140.299720] sd 4:0:0:0: [sdf] 7854080 512-byte hardware sectors: (4.02 GB/3.74 GiB)
[  140.303079] sd 4:0:0:0: [sdf] Write Protect is off
[  140.303083] sd 4:0:0:0: [sdf] Mode Sense: 0b 00 00 08
[  140.303085] sd 4:0:0:0: [sdf] Assuming drive cache: write through
[  140.313204] sd 4:0:0:0: [sdf] 7854080 512-byte hardware sectors: (4.02 GB/3.74 GiB)
[  140.316592] sd 4:0:0:0: [sdf] Write Protect is off
[  140.316596] sd 4:0:0:0: [sdf] Mode Sense: 0b 00 00 08
[  140.316600] sd 4:0:0:0: [sdf] Assuming drive cache: write through
[  140.316607]  sdf: sdf1 sdf2
[  140.322322] sd 4:0:0:0: [sdf] Attached SCSI removable disk
[  140.322426] sd 4:0:0:0: Attached scsi generic sg6 type 0
[  140.327849] sd 4:0:0:1: [sdg] 15523840 512-byte hardware sectors: (7.94 GB/7.40 GiB)
[  140.332506] sd 4:0:0:1: [sdg] Write Protect is off
[  140.332510] sd 4:0:0:1: [sdg] Mode Sense: 0b 00 00 08
[  140.332513] sd 4:0:0:1: [sdg] Assuming drive cache: write through
[  140.344710] sd 4:0:0:1: [sdg] 15523840 512-byte hardware sectors: (7.94 GB/7.40 GiB)
[  140.350346] sd 4:0:0:1: [sdg] Write Protect is off
[  140.350352] sd 4:0:0:1: [sdg] Mode Sense: 0b 00 00 08
[  140.350356] sd 4:0:0:1: [sdg] Assuming drive cache: write through
[  140.350364]  sdg: sdg1
[  140.365065] sd 4:0:0:1: [sdg] Attached SCSI removable disk
[  140.365172] sd 4:0:0:1: Attached scsi generic sg7 type 0

I wonder what's different about other people's configurations, apart from one failure occurring on a 64-bit system?