Dev Build 2086 is out now.
Lion style overlay scroll bars are available in this build. If you're using Lion, then they'll appear automatically based on system preferences. They can be enabled on other operating systems too, using the overlay_scroll_bars global setting. Keep in mind that they won't work as well on anything other than Lion though, as 10.7 provides more information about the scroll gesture state than is available elsewhere.
Over-bounce, the iOS style scrolling-past-the-end, has not made it in yet. As far as I'm aware, there are no exposed APIs for this, unless you're using a Cocoa NSScrollView. I'll wait and see how this is handled elsewhere (it's a problem for Chrome too), but I'll implement a custom version if need be.
For anyone with custom themes, you'll need to integrate the rules for overlay scroll bars: you can see what's needed by looking at the scroll_area_control, scroll_bar_control, and puck_control classes. Mostly it's a matter of copying all the rules that refer to the overlay_scroll_bars setting into your theme, but there are a couple of other bits required too (such as the non-overlay scroll bars setting the blur property to false, to properly handle switching between scroll bar styles on the fly).
Also available for theming is the sheet_list_control, which is responsible for drawing the background when there aren't any open files. Finally, images used by themes are automatically reloaded when modified, which should come in handy.