Microsoft is releasing Windows Vista later this week. But for most people there's no point in running out to the midnight sales to buy a copy. Unless your computer is less than a year old or has a "Made for Vista" sticker on it, most likely the video card in your computer isn't good enough to get the full Vista experience.
As a developer I had the opportunity to try out Vista on my current computer a few weeks ago. Although I was able to successfully install Vista and have a fast enough processor and enough memory, my video card just wasn't up to snuff. At the time I built my computer about three and a half years ago, my ATI All-in-Wonder Radion 9000 Pro was a pretty good video card. Unfortunately ATI doesn't have Vista drivers for a card this old and the drivers they have available for more recent video cards are all in beta. In fact many of the hardware drivers I looked for were either in beta or not available. Windows Vista did have basic drivers for my video card, but nothing beyond a basic low resolution display.
When it comes to Vista, unless you have a very new machine I recommend you hold out until you decide to buy a new computer. Give the developers some time to update their drivers and make sure their software works correctly on Vista. Especially if you have a laptop. From what I've read running Vista on a laptop can drain the batteries significantly faster than Windows XP.
If you still want to run out and get Vista, at the very least run the Windows Vista Upgrade Advisor and find out what will or won't work. When I ran it on my computer it generated a good sized list of programs that "might have minor compatibility issues after upgrading to Windows Vista."