There isn't much reason to upgrade to Vista on your existing computer if XP is working for you. That being said, if/when you buy a new computer it is advisable to switch to Vista not only for continued support, but also for the features it provides.
Compatibility Myths: Fake. Vista is compatible with 99% of programs that XP is. Of course a few obscure examples won't work but most can run native in Vista, or through the easy to use compatibility mode.
Performance Myths: The performance of Vista is directly related to the hardware you use it on. If you're using some 4 year old prebuilt machine, it is unlikely to run well. Most modern PC's, even the cheap $400-$500 ones you get at retail stores) can run Vista well. In relation to gaming, originally Vista performed poorly compared to XP, but that was because the drivers were young. Today, most hardware can run at similar or greater levels in Vista. In the few cases where it does still perform worse, the difference in negligible.
As I said before, unless you're building/buying a new computer, purchasing Vista probably isn't worth the time and money. That being said, it is a great operating system to use, looks very lovey and runs well under half-decent hardware.
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