I'm currently using Windows 7 RC1 (7100) and waiting for 22nd October
I did some test about multi-tasking in this build (7100) and after opened ~80 explorer windows - my windows couldn't open new windows it looks like a very big lag, explorer.exe in Windows Task Manager reach ~350MB RAM usage.
It looks very similiar to this video:
[ame="http://www.youtube.com/watch?v=X4slDVbgVos"]YouTube - Windows 7 sucks at simple multi tasking[/ame]
So I have a question to you - Did you observe the same results/behavior on yours machines? In RC or better RTM
version of Windows 7?