When it comes to resources, Win7 is definitely an improvement over Vista; got 2GB over here and it simply flies. Gaming is a littl emore unstable then XP, but you can't expect anything else from a beta.
Been playing Fallout 3 quite a bit to test it; sometimes the engine won't initialize properly and you get stuck on a black screen. Kill the process in task manager and try again, no problem. Occasional CTD, just like XP, but you can easily play for hours (entire sunday afternoon, for example) without issues. Performance is the same as far as I'm concerned.
AVG: haven't had problems with SH4 yet, but I didn't do anything more then start it up to see if it ran. Think I'll put in some hours this weekend to see if it runs properly.
Been running Win7 for a while now, without any real difficulty. Finally being able to run games in DX10 is a nice addition.