I find it very similar to every other OS upgrade I've been through on PCs (DOS6/DRDOS, Win3, Win3.1, Win95, Win98, Win98SE, NT, W2K, XP, now Vista) including my experience with the server stuff (Novell 2+, NT, WinServer, Unix, etc): there's a lot of good stuff and a lot of "maybe" stuff that seems really bad at first and ends up seeming like a pretty good idea a few years later.
From Win95 through Vista (and even all the way back on Novell 2.1), I've found that I'd prefer to: 1) wait a bit before actually using it too much (now seems good, for example); and 2) turn off many of the new "maybe" features until they seem like a good idea.
So I have UAC disabled and many services turned off, etc. This is the same as with NT and XP, etc.
Vista is SO much better for TabletPC handwriting than anything else now or in the past that it's well worth the trouble if using a pen. Also, the focus of responsiveness over file-transfers and the such is something I welcome on a system that has many, many things open but only one that I'm "using".
I am not using it for my home MC system. I'm using XP for that. My file servers are Linux-based NAS units. All our office PCs (except TabletPCs) remain on XP for now. Office servers are W2K3 or Linux or Linux appliances.
I don't see going the Mac or Linux desktop direction any time soon - especially if they don't get a decent Tablet working really well.