I wouldn't mind at all. After all I'm already using someone else's creations(source anime/music) while I make my AMVs. If there's no editing in part of my AMV that got ripped, then it's no different than using the original footage. If there's some editing/fine-tuning done then I'd be quite honoured that someone found something useful from the stuff I made. If this is done, then only thing I'd like too see is me getting mentioned/credited in some way, be it the AMV itself or video description or whatever. I don't demand this (since, really, I don't mind) but it would be proper and polite thing to do.
Though I'm not in the position to say all this since my AMVs are still mostly unknown and something people won't bother ripping

If something like this happens I'd be more like curious to see what they have done with it than be offended by it.
Way other thing is when someone just takes the AMV, makes a new entry with it and claim it as his/her own creation. That's just sad
