The wheels I'm using have a flip flop hub. I built the bike I've got them on now as a singlespeed, but after trying it fixed, I found out (like many others have) that I like it a lot better that way. After a couple of months, I ended up taking the freewheel off because I was never using it. I recently put it back on for a couple of cyclocross races, but I don't know if I'll leave it on outside of cross season.

I'm thinking about rebuilding the other bike (after replacing all the parts I'm moving to this one) and having one fixed and the other singlespeed.