One of the best things to come from the DVD format is the bonus features. Unfortunately, I fear that once we migrate to downloaded movies and DVDs, HD DVDs, and Blu Ray inevitably die off, the bonus features will be the first thing to go. Either that or it will change to an Xbox 360 style business model where extra content costs extra. Deleted scenes will cost you an extra $2. Featurettes will cost you and extra $4, etc....
But I digress, my point is that some of these features I could do away with right now. At the top of that list would have to be the gag reel/blooper real. Seeing actors flub lines doesn't really entertain me anymore. Sure, there is the occasional humorous ad lib that doesn't make it into the film, but that is pretty rare.
Commentary tracks: The quality of commentaries varies wildly. Some are very interesting. Some are terrible. For example, the Simpson's commentaries are very entertaining. You get to hear about some of the inside jokes, some of the things that were cut or changed, inside information about production and animation, plus a whole lot more. On the other side of the fence was the Conan the Barbarian commentary. I like Arnold Schwartzenegger as much as the next guy, but 2 hours of he and John Milius saying, "oh yeah, I remember that" is not entertaining. But I vote to keep commentary tracks.
Deleted/alternate scenes: one of my favorite features, these have to stay. Usually it turns out there was a good reason that the scene was deleted, but a lot of times some really good scenes get cut for time or pacing. These have to stay.
Featurettes: These are really a mixed bag. It seems like most of the behind the scenes and making of featurettes usually aren't that interesting. Some of the featurettes that give you more in depth information about the story or characters are interesting. As an example, From Hell had a very interesting featurette about Jack the Ripper, with different theories over the years of people who thought he was. More thought should be put into featurettes if they want to keep those.
I could do without any of the following features: trailers - either for the movie on the DVD or other movies, storyboards, scripts, still photos, artwork and concept designs, or music videos.
I've tried to come up with some other special features that I haven't seen on a DVD that might be good, but couldn't come up with anything. I'll keep you updated if I do think of any.