Prediction: 2010 will be the year of game mechanics
I kind of dread this, actually. As with the “now 150% more social!” and “it’s podcast-ic!” trends of yore, hundreds of craptacular “look! It’s a GAME now!” bolt-ons are being designed by committee as I type this.
Adding a “foursquare”-like game to your web service is going to be the hot new thing.
It’s already started with Glue; see Fred Wilson’s post.
Shitty social sites are shitty. Shitty game mechanics in regular applications are shitty.
It is fun to have a score when appropriate. Note that some games don’t have scores. They are about curation of an identity. Games are a huge class of applications.
You should look at this presentation by Amy Jo Kim. She’s really smart.