I too think it's too early to say. I think for current XP users it would be wise to wait for Vista Service Pack 1 to upgrade. I just installed 5744 last night and it seems the builds only get worse. I was perfectly happy with Pre-RC1 5536. And this whole problem with AV's being locked from the core is highly aggrevating. I know, I know, Avast works fine but I can't stand Avast. I like using AVG. It works great on 5536 with UAC turned off. But once you upgrade to 5600 or higher, AVG Resident Shield will not load. It's just annoying that it would work fine in one and then out the crapshoot on another.
I think for an OS that's 5 years in the making, I think they spent too much time making it look "pretty". Don't get me wrong there are some nice touches and I DO enjoy using something "different", but overall, I see it as a better looking XP with provisions for Microsoft to lock other companies' software out to force people to purchase their own.
I currently have 3 PC's, 2 G3 iMacs, and a G4 PowerMac, and everyday, buying a new Intel Mac, looks more and more appealing. This is all my own opinion though. To each his own.