Sidebar is a Hog
If you're having performance problems on your Windows Vista systems, one thing you might take a look at is Windows Sidebar. It is quite badly behaved! I find it is consistently one of the biggest memory hogs and almost always the most prolific generator of page faults.
You'll see hundreds or thousands of page faults per second, even when there is plenty of free memory. Any screen updates in the sidebar (just try running the mouse over it) puts your page faults through the roof. It's particularly bad when displaying a clock with a second hand, which will constantly generate about 400+ page faults a second.
Another place where SideBar will drag you down is if you connect using Remote Desktop Connection. Anything but a blisteringly fast connection will respond like a dawg if SideBar is running on the remote system.