I have had Vista (upgrade from xp) over a year now on my desktop and xp on my laptop.
Vista is fast once you have tweaked the settings and set up readyboost.
http://mostlysavingmoney.com/top-10-windows-vista-speed-tweaks/
I have had less 'glitches' than I did with xp and many long term xp problems vanished when I upgrade from xp to Vista.
Vista is far better once you get to know how to use it (im still learning the odd thing after a year) and I do have to use my xp laptop from time to time but really hate xp now.
Simple tasks in xp require lots of programs to complete.
e.g In Vista. to e-mail say 30 jpeg photos is very easy. Just select all 30 photos and click the e-mail tab, the choose the re-size suitable for the e-mail. Vista auto re-size all photos in seconds and add them to a new e-mail.
In xp I have to re-size each photo and make copy's then attach them one by one to my e-mail. this takes ages.
Lots of examples of Vista being far faster for simple tasks.
My fav. features in vista are all the time saving tools:-
the 'e-mail' button (as above)
the 'snipping tool' (to find it click the >> icon on the toolbar)
windows update (quicker as does not require to run a internet browser)
Windows mail ( i find better than outlook express)
the toolbar tab preview
the very quick search
Vista can handle more ram than xp
readyboost (uses usb memory pen as extra ram)
better security
But im sure 'Windows 7' due out in 2009 will be better again.