I was just thinking last night about this, and it would be great for TV series on DVD. My wife is in love with Sex and the City, we have the DVD collection on MCE, however to watch and episode she has to click on say.. Season 2 disc 3, then use the DVD menu to find the episode. It would be nice to bookmark the start of each episode and have each bookmark named, episode 1, 2, 3 etc and she could just click on the episode she wanted without having to first navigate to the disk.
Of course this would only work if like Collin mentioned, you didnt have to open the Disc to get to the bookmark.