I did notice some texture weirdness going on that wasn't happening a month or so ago so I decided to finally try and track that down. This is when source control is absolutely required! Using my SVN server I was able to easily sync back to old versions of my source tree and build instantly. This allowed me to find exactly when things started going bad. A simple diff later and everything was back to normal.
If you're not using something like SVN yet I highly recommend it. Even if you're running it on the same machine. You don't get the backup properties of source control then but you do get the ability to roll back in time. In this case it saved me hours of tedious debugging.
SVN is open source and does everything you need on Linux or Windows. Add TortoiseSVN as a shell add on in Windows and it's like you're using real software or something.
So go start controlling your source. Do it now! Do it before you need it! I'm living proof that you need it! Beefcake!