I find these projects fascinating - particularly because they make it really easy and interesting for people to make small contributions... rather better than the Wikimedia movement does!

My girlfriend classifies galaxies on Galaxy Zoo all the time, but she finds Wikipedia too big and intimidating to make the smallest correction to.

"Gamification" is a bit of a buzzword at the moment - possibly an over-used one - but these kinds of projects are very good at it.

Chris