Here's an example of what I was talking about if anyone cares: epsilon-not.net/… (a few experimental :target rules I added to the stylesheet)
The scrollbar appears as though it were "outside" the main content element. I have no idea how it looks cross-OS though.
For some reason it's very buggy in firefox, even mousing over it in firefox 3.x will cause the page to flicker, firefox 4 is better, but not completely. Chrome, Opera, and Safari have no problem with it.