Well, I run my own companies, so I like the cutting edge - and we are using Clojure.

A good friend of mine works for one of those big consultancies, however, and they are currently rewriting the backend of the second biggest online retailer of the world and they are using Clojure, too^^

So either I'm getting too old for the sexy Startup business or Clojure is at the same time stable and fancy(;

SBCL (free), Allegro ($), probably some folks are still using clisp (which is a pretty cool Lisp, but almost defunct).

We built kindista.org with SBCL/Hunchentoot.