I don't know why Microsoft is calling the Service Pack cleanup tool a new feature in sp2, It, (or something like it) is in sp1. To run the clean up tool, open an elevated command prompt and type vsp1cln.exe. This gets rid of the files that sp1 backed up during the install and sp1 can no longer be uninstalled.
As Mikey already mentioned, you'll need these files from SP1 to restore your system once the final release of SP2 comes out.
If you remove these files now, you'll need to do a complete re-install of Vista once the final version of SP2 comes out.
IMHO, unless you have Vista installed on a test computer or, as a virtual system, installing SP2 at this point is useless since it
will need to be un-installed and, you'll loose all programs and/or updates to programs before you can install the final release of SP2.
This is one beta you need to be careful of before you decide to install it on your regular system regardless of how we'll the beta behaves.