This might be wishful thinking. At the very least, it is totally subjective. But after the first few days of testing and use, it looks to me like it might really be better than it was any of the times that I previously tried it.
The first thing that got my attention was the speed with which it turns on again after suspending. This laptop (Fujitsu Lifebook S6510) has the optional 1 GB of "TurboMemory", and I can guarantee you that the previous times I ran Vista I could not see anything unusual about the suspend/resume speed. But this time it practically jumped up and grabbed me - after suspending the laptop, I hit the power button and in less than five seconds it is ready to use again. Now, I have updated the Intel TurboMemory driver from the Intel Support Downloads page (no sign of an update on the Fujitsu Support page...), but I did that the last time that I tried Vista also. Whether this improvement is due to one of the recent Vista updates, or it is because SP1 installed more easily this time, and therefore perhaps "better", I don't know.
Next, it is connecting to the Wireless-N network at my house consistently, whereas previously it would invariably be unable to connect two days in a row without a router reboot. Again, I can't be certain this is because of an improvement in Vista, because I have also changed the wireless router in my house. I know for certain that the fact that it is connecting consistently at a higher speed is because of the router. But either way I suppose this indicates that Vista and the things around it are getting better.
The other thing about Vista this time is that it just "feels" more stable. I haven't had any crashes yet (what is this for a world when we think we are doing good by going three days without a crash?), and perhaps more indicative, I haven't had any programs hang or permanently "stop responding". Everything that I have installed so far has gone smoothly, and I haven't gotten the "that program might not have installed properly" question from Vista yet. Performance is still not as good as Ubuntu or Mandriva on the same laptop, but even that still seems better than before.
I know that we all love to bash Microsoft in general and Vista in particular, but maybe Microsoft really has finally improved Vista - to the point where it is the way it should have been 18 months ago, when it was released. I am still primarily using Linux, and only run Windows during my morning and evening commute, but I will at least continue to run Vista rather than XP for a while, and see how it goes.