microsoft emphasizes that their next OS will come out way sooner than vista came after xp (meaning, much less than 5 years). i personally believe it's best just to skip vista. say 3 years down the road ms will come out with a new one. by that time you'll want to upgrade your hardware anyway, etc. plus it seems that vista isn't going to be too successful. so MS will do their best to make up for it with the next OS they'll release. same was with windows ME (possibly the worst OS that MS ever released), which was followed by winXP (possibly the best one). just sit vista out guys. don't waste your time, energy and money.
by now it is obvious to all that vista provides literally zero technical benefit over xp anyway. we all got better stuff to do than to mess around with it.