For the people bragging up Vista, let me ask you this.
Did you load the operating system on a PC you had, or was it a new PC with it already loaded? The reason I ask this is there's a multitude of things that can slow down any PC and a fresh system will almost always seem faster.
bought a new pc on black friday that came with vista. Its very fast and all my programs are working perfectly. (im a software engineer so you can imagine the geeky stuff i have on it)
I am actually a big proponent of some of the features of vista, however for the average computer user i would think vista would be very overwhelming and confusing. Do i get annoyed with the ridiculous security measures on vista? yes, but i also greatly appreciate knowing exactly whats going on before the system writes to the registry, etc...
If you know what your doing or are not afraid to learn a little more you might be best suited to get vista. Xp is a very stable OS and you really wont loose anything going that direction.