I can agree with XP running smoother. It's no secret that it is a much more stable OS than Vista.
But for those who choose the later, there are tricks and tips on how to make it more or less faster. It also depends (once again) what you use the PC for.
Though it won't run as fast as with XP would with the same specs, it might be worth it.
Pretty easy way to start is to close Aero, as an example.
Then we have SP1. For some it works great... for others... ah well.
But really, for those who wants to continue with Vista, and wait untill Windows 7 rather than go back (or up) to XP, it's just as I said.
Go to your search engine and type like... "10 ways to make Vista faster".
You should atleast get some things you didn't thought off.