I tested this on both Windows and Mac across a few browsers.
Chrome on Windows doesn't autoload with the scroll bar itself, however it does with the arrow button at the bottom of the scroll bar.
Chrome on Mac doesn't work with the scroll bar at all (including the arrow button).
Internet Explorer on Windows doesn't autoload with the scroll bar itself, however it does with the arrow button at the bottom of the scroll bar.
Firefox on Windows and Mac works. The autoload doesn't happen until the mouse button is released.
Safari on Mac works.
Keys (page down, down arrow, end) worked on all browsers. Scroll wheel also worked on all.
Windows 7 - Chrome 9.0.597.86 beta, IE 8.0.7600.16385, Firefox 3.6.13
Mac 10.6 - Chrome 9.0.597.84 beta, Firefox 3.16.13, Safari 5.0.3