I personally feel this is the biggest change to the core Windows architecture since 3.1 -> 95. As such, I'll be buying it for my main rig somewhere around the end of Q1 next year, and I likely will not be upgrading any of my current hardware to do it.
4Ghz Prescott, 2GB DDR533, 500gb of drive space, DVDR and CDRW, 7900GT 512mb video, Envy 24PT audio and a CSA-connected gigabit Intel nic are going to be just fine... I'll probably even buy two copies so my Dell E1505 (Core Duo, 2GB DDR667, 80GB hd, DVDRW, 7300Go) can have one too, albeit a "lighter" copy more than likely compared to my desktop.
I've spent the last three weeks with Vista RTM on a Dell Optiplex 620, my Dell E1505 listed above, and an IBM R50 (1.7g banias core, 2gb ram, 40gb drive, DVDR, intel nic, ATI 7500 mobility 32mb) with zero issues. It boots faster than XP, it launches my apps faster than XP, it is far more responsive on my single-processor machine when doing intensive tasks, my battery life on both laptops got better and app compatibility on the stuff I use is just fine.
I still see people bashing Vista for being "slow and bloated and cumbersome and glitchy" and then in the same breath state they're on Build 5280 or RC1 or something. Maybe those of you who aren't using or trying the RTM should re-try and see what you've been missing.