Reading posts like this has me seriously considering skipping the 10.6.7 patch altogether on my 11" MBA. All I can figure is that Apple must have modified the NVIDIA GeForce 320M drivers for the worse. The much worse.
We'd need a more complete set of benchmarks to make that conclusion. Anyway, note that Apple did say that 10.6.7 was geared both to address performance and an issue that could cause a kernel panic. I was getting panics left and right (though Apple's solution was to replace the logic board), so perhaps they throttled down the 320m because it was causing issues.
Anyway, they'll definitely need to patch either 10.6.7 or iTunes 10.2.1 to fix the iTunes issue, so hopefully they address any performance issues, as well.
I did notice this, though:
http://us.battle.net/sc2/en/forum/topic/2267599143
http://discussions.apple.com/thread.jspa?threadID=2795016&tstart=0