I have learned a few songs in Drop D. You can play "Can't Find My Way Home" in either standard or drop D. He uses Drop D in that new video but it sounds fine in standard tuning too. He's playing other chords and moving the bass notes up to take the alt tuning in the low E string into account. It sounds complicated but it's not once you understand it.
It makes playing in the key of D sound really cool. I know a couple of other songs in Drop D, "Dear Prudence" by the Beatles, and a song I learned at Fur Peace, Roy Book Binder's "Another Man Done a Full Go Round" a really great song that's incredibly fun to play. Also, Jorma Kaukonen's great instrumental "Embryonic Journey" is in Drop D. JIC you don't know it, http://www.youtube.com/watch?v=KqKH8KJ4h4Q&feature=fvst
Drop D is worth playing around with, it's a pretty cool deal, I plan on further explorations with it. Really easy to get to, also, just one string retuning, the low E.