I've been going through this this morning. It seems that the CPU loves to go up to 1.2GHz even if it doesn't need to be that high (and it stays there). Also there I've also been noticing through ADB shell that their are a few niggles. For example the wi-fi sharing process can start without even being activated.
For example this
was a ADB shell top taken while running Cordy downclocked to 800MHz in setcpu. The phone was a tiny bit warm but only by the camera (where the CPU is). Basically, this just shows that if you are playing a game, nothing else is going on so the CPU shouldn't be going up to 1200MHz. And it plays the same as when it isn't underclocked.
I'm currently assisting Pulser with investigating this until he gets his SGS2.