What? Nobody else wants to comment on FOAM tires?
Well, I'll chime in.
During the summer months we run on an unprepared asphalt parking lot. We all run foams, not because of a requirement, but because they are faster. Several people have tried rubber, but none have been able to keep up.
We usually run Plaid front and Purple rear, but there has been some recent experimentation. Some run Double Purple front and Purple rear, others have tried a Pink / Double Pink combination. I have also heard of the Cyan / Tan combination (from TRC).
In stock, I usually get a minimum of 4 weeks out of a set of tires. That includes several practice runs each race day. Usually a total of about 7 runs per week.
Those that have tried rubber noted that the tires lost a lot of their grip after a couple of runs. While the rubber may last, it wasn't competetive the vast majority of it's life. With foams, their grip remains fairly constant through their entire life.
Jeff Gilligan