Wow. I didn't know you could reliably test performance on a beta.
Anyway, I seriously doubt MS will force people to have 2gigs of RAM to run Vista at an acceptable speed, when the current average is between 512 and 1gig, and will probably be so for the next half year at least.
But let us not forget...There were plenty of people complaining about the "massive and impossibly huge" requirements of XP when it first came out...which mostly turned out to be bunk.