I've been using Vista for quite sometime now. There are issues when it comes to application compatibility (Not MS's fault). Some of the applications I use never bothered to be updated for Vista. And there's the fact that it's a bit more resource demanding that Windows XP, And so on and so forth. Fact is it comes down to the user. After a couple of months, I got used to it, and found ways to make everything work out. I'm happy and can say that Vista is working out great for me. I've been recently toying around with Windows 7 from the RC to the now infamous RTM and all I can say is, it's the best I've ever worked with in early development.
Oh and on a side note. A company that I was affiliated with a couple of years back (Dell) used Windows Vista on some of their terminals, but still retained Windows XP for most of them.
Back to the topic. Windows 7 is the first time MS released something that actually didn't scare me to actually install, although I'm keeping my Vista on my workstation (due to application compatibility, most of the applications I use for work already have support, just don't want to take any chances). If I do get enough cash and get a laptop (been planning for almost a month now), it will surely be using Windows 7.
For me, it combines the visual enhancements (and some addtions at that) of Windows Vista, and the resource friendly application compatible Windows XP. I've installed and tested Windows 7 Ultimate on a friend's Desktop (his 30 days are almost up) and he's very pleased with it (he's an average computer user). In my opinion, if you have the means to, go ahead and upgrade.
I love win 7 but i dont know if i can be bothered with the hassle of changing over (or the cost)
i use the wifes all the time though 
