I'm on Ubuntu and scrolling with the mousewheel feels like I'm scrolling through tar. A lot of these sites with fancy scrolling hooks seem to do the same, really annoying.
I think it's fine to hijack the default scrollbars so long as all you change is their appearance. If you can't do it without changing the way scrolling via the wheel feels in any way, you need to trash it and use the default scroll bars.
Maybe it's designed for people with touchscreens? On Windows, in Chrome, the scrollwheel sucks, but if you click the page and move the mouse up or down to scroll (dragging), it's much more responsive.
