EC is an interesting mix of theory/AI/economics and many other things as well (data mining, social computing, user interfaces....) Definitely a bit of a hodgepodge, but interesting in its variety. If you don't look at the titles/abstracts ahead of time, you never quite know what the next talk will bring. (Maybe I should be looking at the titles and abstracts ahead of time...)
Some quick highlights
Giorgos Zervas gave the talk on our Swoopo paper.
Rahul Sami gave an interesting talk based on the idea of dealing with external incentives in mechanism design settings.
Ramesh Johari gave a talk about a simple model meant to abstract the competing effects of network effects and congestion.
Sven Seuken talked about market design and analysis of a P2P backup system.
I'm sure there were other interesting things, but I was in and out of sessions at times.