Yeah, although not officially announced yet, it looks like a new version of Couchsurfer that works with the 2.1 AppleTV firmware is available. Check here for the download, you will want the file called couchsurfer-0.4-2.1-bin.tar.gz. I tested it and so far it looks like it is working just fine. With the 0.3 version I had crashes and the bookmarks & history did not work. That's all fixed. What I did not test yet is add the flash plugin, but I guess that will work also (will update you on that later).
Update: installed flash (and other plugins), tested youtube.com and as expected it works.