I have two ss, one an old Trek 10 speed set up with fixed gear, the other an old Schwinn 10 speed set up with single speed (BMX) freewheel. The Trek has a low-ish 39/17 gear for spinning while the Schwinn has a higher 48/18 for higher speed/slighty harder work. I love them both. Everything everyone has said is right. As Oscaregg says the fixed gear puts you firmly in touch with the road. It is hard to explain what that means until you try it.

I got interested in fixed gear/ss from reading Sheldon Brown's articles which I highly recommend, especially for fixed gear. Learning to ride fixed gear is not hard, but it can dump you on your butt immediately if you don't have at least some idea how to start off.
FWIW,
Raymond