Zen is the silly rant people who ride fixed give when they don't know how to explain what they like about riding fixed. When people ask, just say it's fun-- it's not profound, it's not unique, and it certainly has nothing to do with Buddhism.
Lots of people here do tricks. I mess around with whatever tricks can be done while actually going somewhere on the bike, but I don't really just ride in circles messing around much. Just not that exciting to me personally.