So you limit the number of times you can be rated per day.
The problem is that there's no way around abusing the system. No matter what system you put in place, people will find a way to abuse it. The best course of action is to find a system that is the least abusable.
In fact, I wouldn't mind a system like what I proposed, that allows me to only look at the rankings my friends have handed out. That way I only see players who my friends have rated and who's rating I trust. So it doesn't matter if JoeScrub created 100 accounts to rate up his buddy. That rating means nothing to me because my friends rated him properly.