Comment 3 for bug 742134

The maximized window case is certainly the most evident. One may even call it a regression wrt normal scrollbars (just try maximizing and scrolling in firefox right now ;P )

A second case that comes to mind is when you approach the scrollbar from the right. In this case, in order to catch the thumb one has to:
1) reach and hover the pager (because the mouse pointer was at the right side of it)
2) move back of a couple of pixels to catch the thumb

This could be solved either by making the pager draggable, or by making the thumb appear on the left when approaching the scrollbar from the right side (which I guess would qualify as a separate bug).