OK, so I followed the instructions on the DebuggingProgramCrash page to get a backtrace, and had some difficulties, since the Bug Buddy kept popping up and interfering.  I seem to have found TWO issues instead of one, as the gdb logs will indicate.

The first time, I ran gnome-screenshot without the --disable-crash-dialog flag, and found it very difficult to reproduce the error.  I ran into two issues.  The first is that intermittently, I would get messages in gdb that said there was an unexpected async reply:

(gdb) run
Starting program: /usr/bin/gnome-screenshot 
[Thread debugging using libthread_db enabled]
[New Thread -1224685904 (LWP 5669)]
[New Thread -1235620960 (LWP 5672)]
[New Thread -1244013664 (LWP 5673)]
Xlib: unexpected async reply (sequence 0x601)!
[New Thread -1263416416 (LWP 5675)]
[Thread -1244013664 (LWP 5673) exited]
[Thread -1235620960 (LWP 5672) exited]

Program exited normally.

When this happens, I am unable to close the gnome-screenshot dialog, and I am forced to kill the process manually before the window goes away.

Now, I did get the segfault crash eventually, but the bug buddy popped up and I was unable to get a backtrace in gdb.  Here's what the bug buddy had in the window:

Memory status: size: 57683968 vsize: 0 resident: 57683968 share: 0 rss: 11218944 rss_rlim: 0
CPU usage: start_time: 1173286442 rtime: 0 utime: 20 stime: 0 cutime:20 cstime: 0 timeout: 0 it_real_value: 0 frequency: 0

Backtrace was generated from '/usr/bin/gnome-panel-screenshot'

Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread -1225202000 (LWP 5214)]
0xffffe410 in __kernel_vsyscall ()
#0  0xffffe410 in __kernel_vsyscall ()
#1  0xb746734b in __waitpid_nocancel () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb7f241b6 in gnome_gtk_module_info_get () from /usr/lib/libgnomeui-2.so.0
#3  <signal handler called>
#4  0xb739537c in memcpy () from /lib/tls/i686/cmov/libc.so.6
#5  0xb725ae8d in ?? () from /usr/lib/libz.so.1
#6  0x08210178 in ?? ()
#7  0x0824bbe9 in ?? ()
#8  0x000001c0 in ?? ()
#9  0x00000014 in ?? ()
#10 0x00000105 in ?? ()
#11 0x08208178 in ?? ()
#12 0x00008000 in ?? ()
#13 0x00008000 in ?? ()
#14 0x00010000 in ?? ()
#15 0x00007efb in ?? ()
#16 0x000001c0 in ?? ()
#17 0xb7269a10 in ?? () from /usr/lib/libz.so.1
#18 0x0000fefa in ?? ()
#19 0x00000000 in ?? ()

Thread 1 (Thread -1225202000 (LWP 5214)):
#0  0xffffe410 in __kernel_vsyscall ()
No symbol table info available.
#1  0xb746734b in __waitpid_nocancel () from /lib/tls/i686/cmov/libpthread.so.0
No symbol table info available.
#2  0xb7f241b6 in gnome_gtk_module_info_get () from /usr/lib/libgnomeui-2.so.0
No symbol table info available.
#3  <signal handler called>
No symbol table info available.
#4  0xb739537c in memcpy () from /lib/tls/i686/cmov/libc.so.6
No symbol table info available.
#5  0xb725ae8d in ?? () from /usr/lib/libz.so.1
No symbol table info available.
#6  0x08210178 in ?? ()
No symbol table info available.
#7  0x0824bbe9 in ?? ()
No symbol table info available.
#8  0x000001c0 in ?? ()
No symbol table info available.
#9  0x00000014 in ?? ()
No symbol table info available.
#10 0x00000105 in ?? ()
No symbol table info available.
#11 0x08208178 in ?? ()
No symbol table info available.
#12 0x00008000 in ?? ()
No symbol table info available.
#13 0x00008000 in ?? ()
No symbol table info available.
#14 0x00010000 in ?? ()
No symbol table info available.
#15 0x00007efb in ?? ()
No symbol table info available.
#16 0x000001c0 in ?? ()
No symbol table info available.
#17 0xb7269a10 in ?? () from /usr/lib/libz.so.1
No symbol table info available.
#18 0x0000fefa in ?? ()
No symbol table info available.
#19 0x00000000 in ?? ()
No symbol table info available.
#0  0xffffe410 in __kernel_vsyscall ()

I don't think this is helpful.

Next I ran gnome-screenshot with the --disable-crash-dialog flag, and while I could not get a gdb backtrace, it *did* generate a crash report in /var/crash with a LOT of information in it (1.7 MB worth).  I think this will be a much more valuable set of information.  Nothing out of the ordinary was seen in the gdb text output, other than potentially the fact that some threads are not appearing to exit, but not sure if that's an issue.

I've attached the crash report for your perusal.  Thanks so much for your help!