I'm trying to reproduce it now by copying one of the images many times into the same directory.. the directory with images is already 8.4GB, but right now not slow at all:

while :; do cp -v 01-20100831103933-00.jpg $(date +'%s%N').jpg; done
By the way. I'm running Debian stable on this server.

Linux deimos 2.6.32-5-686 #1 SMP Sat Jul 24 02:27:10 UTC 2010 i686 GNU/Linux