Here's how to get the scrollbars installed:
~$ sudo add-apt-repository ppa:ayatana-scrollbar-team/release
~$ sudo apt-get update
~$ sudo apt-get install liboverlay-scrollbar-0.1-0
I got the instructions from this post, but current releases of the overlay scrollbar no longer needs you to set LIBOVERLAY_SCROLLBAR=1 for things to work. Simply restart your Ubuntu machine after installing and supported applications should start using the new scrollbars right away. Yes, you read that right. Not all apps use the new scrollbars, yet.
Post Beta 1 updates
If you update your Natty install frequently, then you should already realise that overlay scrollbars are now a part of Natty by-default. That means you don't need to install the PPA packages to get in on the action.
Users that stick to milestone releases should, of course, get the updates in Beta 2 coming later this coming week. So, only install the PPA packages if you really can't wait.
Upgrading to Natty Beta 1
btrfs is now available on Natty