I am always looking for nice littel design things and of course the infamous scrollbar ist one of these things which many people like to have differen. Well, I have done many sliding DIV TAGS inside of DIV TAGS and whatnot. But while surfing around once again I stepped over this Website:
They have some nice scrollbar treatment as well as some other neat little things (Checkbox and Form Styling, etc.).
So, before you start writing your own, have a look to see if there isn’t already something usable out there.