I have been working with the WordPress.com themes on and I can definitely say that if you are not sure what themes to use on your WordPress-MU/BuddyPress system, try using the same themes they use on WordPress.com. It is easy to get hold of them, they are available via Subversion. You will need a subversion client to check the files out of the repository. Here is what I suggest you do:

1. If you are running Windows then download and install the subversion client called TortoiseSVNotherwise pick one of the following:
   1. Subclipse (Eclipse)
   2. Subversive (Eclipse)
   3. SCPlugin (Mac OS X)
   4. RapidSVN (cross-platform)
   5. AnkhSVN (Visual Studio)
   6. VisualSVN (Visual Studio)
   7. …more clients…
2. To read some about using subversion try these documents:
   1. Mailing Lists (non-subscribers can post)
   2. FAQ (Frequently Asked Questions)
   3. Subversion Book (complete online)
3. On you Windows PC you will add a new folder, then you right-click the folder and look for the TortoiseSVN option that says “SVN Checkout”
4. The TortoiseSVN Checkout windows pops open and you need add the URL of the repository = http://svn.automattic.com/wpcom-themes – Click OK, then click YES
5. It should take a while to download the themes, but its worth it!
6. Upload all the themes to /wp-content/themes like you normally would.

My suggestion is that the WP.COM themes be added to TestBP.org, it might encourage some of the testers to using the blogs more. I read a post on the forum the following about making a theme BuddyPress aware:

Yes, any theme you use with BuddyPress will need a plugin-sidebar.php and plugin-template.php file. It’s used to add dynamic functionality and new pages to the theme without having to drop in new template files. The settings menu and pages are examples of this.

Is that all that is needed or is there more? Any out in the community got any experience with that type of thing?

Note: Image Credit