Gaming the Vote by William Poundstone is a great book I read recently. He's explored virtually every voting system that's been tried and analyzed them. Everything from political elections to web site voting systems is covered. (hotornot is discussed at length). I highly recommend it.
The two "voting systems" you mentioned seem to me to serve two different purposes: voting and rating. Voting up a question means something different than rating a product 5 stars. Voting up/down seems to make more sense on a site like SO or Digg, whereas rating something with stars is probably better applied to a product or a song.
Having said that, I would think stars are more readily understood by more people.
I want to point out that if you have dealt enough with the iPhone app store, you will notice that a lot of users vote opposite (1 star instead of 5 stars) of convention with a clearly glowing review. At first I thought this was an abnormal occurrence but I've seen it hundreds of times now.
So the "up tick" vs "down tick" style makes a lot of sense in light of that trend.