The idea of having an "edit your own movie" is simply silly because I don't know too many people who would seriously invest time in editing a feature length film (except for actual film students/freaks like myself). Editing your own little trailer would be cool.
It would definitely be a neat feature to use with a real editing suite like Final Cut Pro, or something like that. But that's just me dreaming...
Personally, the new format will prove to be very fascinating, and I look forward to DVD producers really flexing their creative muscles with the added capabilities.
Ben_ i think you are right. Yet, I for one, love to buy movies with all the extras and I have yet to view them all. In other words, people will be attracted to the option but may never use it.