Well, as a professional repairer of PC's I am kind of forced to use Vista. People are gonna use it (they'll be forced to if they're buying new kit) so I've gotta know it 🙁.
I've had the RC1 on my main PC since around October and it's been fairly good. I've just gone last week to Vista Home Premium, but I've kept the PC dual-boot: XP is the default OS and sits in one partition, Vista sits in the other.
Most programs I use do work, I have to say. This includes the usual M$ products, the Adobe Suite (photoshop, indesign, dreamweaver etc). The only thing I have a problem with is NetDrive and my HP Printer Software which won't work. It also won't work on XP now since I installed IE7 which botched all the scanner software - and there's no fix for it at present from HP or M$.
However, I would recommend anyone using trading software to stick with XP for the time being. M$ have promised support for XP until at least 2011, and it is one of the most stable M$ operating systems to date in SP2 guise. Nothing like as stable as Linux or Mac OSX, but I'd wager that not many of you have had huge problems with XP for some time; most of the stuff I repair are due to user errors, rather than OS errors.