Machine Specs:
OS: Mac OS X 10.6.7, Macbook Pro
RAM: 4 GB
Video Card: NVIDIA GeForce 320M
Processor: Intel Core 2 Duo 2.4 Ghz
The problem:
Sometimes while playing the game, my graphics will go all... "wonky". You can clearly see what I'm talking about in the picture, especially around the text and the party button. It's still playable, but it is frustrating and requires a restart of the client to fix. Changing resolutions, graphics options, etc. all had no effect. I'm not entirely sure when this happens, but I think it's when I load a new map. Any help with this is appreciated.
It almost looks like what happens when the fan on your GPU starts to go south, causing it to overheat. Try rolling back your drivers to a previous version and see if that fixes it; if not, investigate your GPU's functionality.
But, before anything else, make sure you're using the latest version of java.