Would limiting to 1 vote per ip be that bad? Lots of NAT on the internet these days but it'd be a quick fix. Or maybe allow negative voting, with weighting based on your star rating?

Well we have already ran into some situations where roommates are all behind one router. I actually have that situation at my house. Also public wifi hot spots could become a bigger concern in the future as the site continues to grow. We are almost at 1,000 members in side of 7 weeks with no signs of this abating any time in the near future.

We have thought about maybe limiting it to 3 or 4 ip's per video. For the time being it's enough that we check this site religiously, and have a sharp eye and some scripts for identifying such abuses.