I have to admit that I haven't really delved too deep into the DVD. I've only looked at the trailers, TV ads, music video, and one of the deleted scenes (OK, i've also looked at the outtake clip). So far I think the gag reel is the best thing on the disc. It's not as long as I thought it should/would be, but I dig those multiple shots of R2 falling over, running into people, things, etc.
I may change my mind once I see the documentary features.