I've liked Windows Vista, but then again my machines were far overkill for anything that will slow down XP.
I have three primary machines that I've upgraded to Windows Vista. Everything seems to be running much more smoothly than it did on XP (however, XP ran fine as well).
I've not had many issues in terms of compatibility, sans a couple of printers. They needed upgraded anyway.
Two of my machines I've upgraded from XP Pro to Windows Vista Ultimate, and one of my machines I've upgraded from XP Home to Windows Vista Home Premium. I've been satisfied with the performance and reliability of all three. I've yet to have a total system failure (STOP error), nor have I had a reason to reboot any of my systems from any quirk. My most powerful machine ran for 6 weeks and 2 days without a reboot until I had to power it down to relocate it. That was a sad day. The longest I've gotten XP to run without requiring a reboot for one reason or another was just over 5 weeks - I would at least have to restart explorer.exe - and I didn't even run Folding@Home on XP.
All through my 6 weeks, 2 days of uptime, I had Folding@Home running on one entire CPU core (along with Folding@Home on the PlayStation 3 for that entire time period (aside from some gaming), also not requiring a reboot). The system still ran fast enough to play Oblivion with high detail, high resolution and not noticably drop frames nor glitch.
I use Internet Explorer as my primary web browser (requiring more "resources" than other browsers such as Firefox), and generally do NOT use the tabs. I've had it say numbers as high as 43 - Internet Explorer between forums, class work, and windows I neglected to close through that period. I had 97 processes running also in that period, taking 1.5GB of physical system memory. Not a hiccup.
Also, "DWM", the window manager that Windows Vista uses I've only noticed taking about 40MB of system memory MAX with Aero Glass (with the bulk of the visual handling passed to the graphics card). XP's on the other hand I've seen taking as much as a couple hundred megabytes, JUST for the "Windows XP" look. There was no window transparencies NOR "FLIP 3D" type stuff in XP.
I've been extremely happy with it. I've been running it since launch, actually.
Furthermore, I've been extremely happy with Microsoft Office 2007 as well - I've upgraded all three of my systems with that as well - from Office XP on one, and 2003 on the other two.
I say: "Way to go, Microsoft".
If your system has issues running Vista, upgrade your RAM. My lowest system has 1GB of RAM and runs it with the least performance (but still well). The rest of my systems, with 3GB+, run it with excellence. RAM is pretty cheap at the moment.