Patrick Stach has announced that he has created a program that can find MD5 hash collisions in 45 minutes on a 1.6 ghz Pentium 4. If that's true, MD5 isn't just insecure, it's downright dead.
If you've got any digital signatures using MD5, I suggest you FIX THEM, NOW! (not that I know exactly what to use; SHA-1 is on its last leg)
UPDATE: Fortunately, it isn't as bad as I thought it was. This program can only produce two randomly generated messages that hash to the same value; it cannot find a new message that matches a given hash. No complete security meltdown yet, but you could still safely say that MD5 is no longer safe to use.