Preston, speaking as a long-time senior developer, I have some major issues with Vista, and I'm using Beta 2. The sheer memory overhead and disk requiements are staggering. UNIX has so many under-the-hood advantages compared to Windows, with less of the bloat.
Also, they really mucked up the UI with Vista. Oh, it's real cute, and that's the problem, it's too cute. You have all the cuteness contributing to the overhead issues, for what - aesthetics?
And UAP/UAC? Please, don't get me started. Paul Thurrott is being overly kind in that regard. The implementation while far less annoying in beta 2, continues to be a major joke for really no good purpose other than to make poor old Grandma feel more secure. How about this: I WANT full Admin rights without all those silly prompts, so what's wrong with that? I'll tell you - Microsoft has decided I no longer need it. Sorry, not good enough, I've been doing this for way too long for some neophyte at Microsoft to tell me how to practice safe conputing.
Come on, an OS is supposed to boot the system and facilitate system I/O, more than that is nice, much more than that is bloat. Near as I can tell, there is no compelling reason to upgrade. WinXP for all its problems is good enough.