I recently upgraded to 12.10, and my scrollbars disappear, being replaced by some funny floating thing that looks like a bandaid. Granted, I think I recall having this same problem and fixing it last time I "upgraded," but that was a year ago or so.
Following the instructions on some website, I disabled "overlay-scrollbar" or something like that in synaptic. That fixed the problem for most, but not all programs.
To wit: the scrollbar in evince (and a few other programs) is still very strange. Though not as bad as the "floating bandaid" version, the slider (or what you drag in the middle of the scrollbar) is very, very thin, so trying to click on it is essentially pixel hunting. Also, there are no arrows at the top and bottom of the scrollbar, and clicking on part of the scrollbar moves to that part of the document (instead of advancing a page which is the accustomed behavior).
I would really like to fix this because it has made evince unusable. I've been using acroread as a backup but that is in so many ways an inferior program. Any help? Firefox, and most other programs, work fine since the overlay was removed. But I would just like to be able to have normal, functional scrollbars on all of my windows/programs.