Personally, I think personal DVD-writers are mostly a waste of money. If you're backing up 8-gigs of data all the time (and you aren't a high-end video/sound editor without a storage base) you need to rethink some things. If you're constantly running back and forth with gigs worth of data, as part of your daily process, I would suggest finding a different transport alternative (like an external HDD) where you can cheaply and readily change data.
Making DviX copies of movies (without owning the movie) is illegal, so we won't touch on that.
And the whole "making backups of my movies" is a bit loopy in itself. There's nothing to prevent harm or theft from coming to your "backup" collection, too.
My entire backup load at work is under 2 gigs, and we use tape and a HD-DB storage bank for that. Even IF we used discs, I'd just burn 2 CDRWs at a cent a pop and be happy.
I'm just rambling, but it just seems funny to me. I don't know. Files and programs keep getting bigger, but I still don't see the need (outside of professional use) for making DVDs left and right.