I got my 24" 13 days prior to the update, and I opted to get a $200 refund rather than driving back to the store, paying the restocking fee, and getting the updated model. (Not to mention how much time it would have taken to backup, nuke, and reinstall the returned computer, then restore all my stuff to the new new one.)
I'm happy with how Oblivion, The Orange Box, and Bioshock run. I don't run at max res, since 1920x1200 is a very high resolution, I use 1280x768 with 2x AA and most settings at max. They play fine. I don't have UT3 or Crysis though.
I've been doing most of my video gaming on the Wii and XBOX 360 anyway, so I'm satisfied. If you're a hardcore PC gamer, well, Macs just aren't for you. If you're just a gaming geek like me, though, the iMac is just fine.