I usually run SPD's on all my bikes, but on the fixed it didn't seem to work to well for me. I would sometimes unclip (granted this is my faulty technique probably) but that wouldn't happen too much on the geared bikes. I am currently trying out some Time ATAC Aliums, and so far so good. It has a little more float and seems to be just a little more robust than SPD's. It is also a little wider which is nice, it just feels more solid than the Shimano's, esp when back pedaling and skip stoping.

P.s. I am not a trickster, I just like to haul ass with a fixed on public roads with little traffic and lots of lights. I do run a brake, and it does get used, but sometimes it is wise and very fun to test yourself and your skillsets on the bike. ATAC's inspire a little more confidence in this setting IMHO.