I haven't been able to pin down exactly when this happens, but with CVS HEAD, eog seems to occassionally hang when trying to close it from the X in the titlebar.  I did an strace and managed to reproduce it:

Here are the last lines from the strace output before it hangs:

poll([{fd=6, events=POLLIN}, {fd=11, events=POLLIN|POLLPRI, revents=POLLIN}, {fd=12, events=POLLIN|POLLPRI}, {fd=13, events=POLLIN|POLLPRI}], 4, -1) = 1
read(11, "GIOP\1\2\1\1$\0\0\0", 12)     = 12
read(11, "p]\322\277\0\0\0\0\1\0\0\0\1\0\0\0\f\0\0\0\1\1\1\1\1\0"..., 36) = 36
gettimeofday({1154837164, 998841}, NULL) = 0
gettimeofday({1154837165, 3500}, NULL)  = 0
gettimeofday({1154837165, 18857}, NULL) = 0
gettimeofday({1154837165, 21849}, NULL) = 0
gettimeofday({1154837165, 24521}, NULL) = 0
munmap(0xb46dd000, 1376256)             = 0