I can't believe no one else has seen this, but I searched the forum and didn't pull up anything similar, so here goes:
After playing for 10-15 minutes, the messages, numbers from health etc. start sticking onto the screen persistently. It looks like you've just driven through a cloud of bugs and they're all stuck to the windshield. This is especially bad with Oak as all the creeps and minions have +40's popping up constantly.
This is on Vista x64 on a GTX 260 with the latest drivers (181.22). It seems to only happen when I have AA turned on. I've also seen it on other boxes with AA off, though that was in earlier betas.
Anyone else seeing this?