Noticed today that I wasn't getting accelerated 3D on my desktop. This was causing a number of problems, the most significant one being it stopped Wine working. I tried to investigate by running glxinfo but just got a stream of errors like:

API ERROR: could not register entrypoint for SelectTextureSGIS

I tried fglrxinfo with similar results, strangely when I tried as root I got no errors for either, so I'm thinking it's some sort of permissions snafu. I tried changing the DRI mode in xorg.conf but that didn't help so I had a quick Google for the solution. Found a few posts in an Ubuntu bug database which led me to a forum post which suggested swapping the libGL.so for an older version. I didn't want to use the version posted on the Ubuntu forum so I investigated the files I currently have, and it turns out I have two copies: one in /usr/lib/fglrx/lib and one in /usr/X11R6/lib/. I decided to try linking the one in /usr/lib/fglrx/lib to the one in /usr/X11R6/lib/:

cd /usr/lib/fglrx/lib
rm libGL.so.1
ln ../../libGL.so libGL.so.1

I exited KDE and logged in again (to restart the X server) and 3D acceleration is back!