When I play on "low performance" (9400M) I have to have 800x600 res, and then it's sort of playable. It's ridiculous though because I'm so slow in some parts that I'll have died before I even see any enemies... NOT COOL!. Some boss fights I literally can't do anything (all of act IV pretty much) because I'm too slow to be of any use to my party.
When I switch to "high performance" (9600M GT) then I get about 10 seconds of great 1440x900 awesome sweet smooth gameplay - and then it freezes. Woohoo! I have to wait about a minute for it to tell me I either got disconnected or the whole program quits.
I've done everything - Reset the SMC, repaired disk permissions, quit all but the essential programs, I've even done a complete fresh install of lion, all the updates, the combo update, did I mention it's all on a SSD? So there should be no read time issues..
I understand bad resolution with the 9400M, but what's the deal with the 9600M GT? I don't get why it keeps freezing up. Please help Blizzard! I love this game! and want to be able to play it and be useful.