With the recent glibc from 7.3 debuging threaded apps doesn't work.
[New Thread 2049 (LWP 3394)]
Can't attach LWP 3402: Operation not permitted
I get this with both nautilus and mozilla.
I tried backing down gdb, glibc and the kernel to 7.2-ent and 7.2-errata
versions, and it the only thing that seems to break is when i use the 7.3
glibc (I tried 2.2.5-30).
Fixed in glibc-2.2.5-32.