I'm a lispworks user for a few projects. The killers, generally, for an enterprise project are the smaller binaries and java interface. I know of a few places that write gui apps in lispworks, but many (most?) projects with a user interface use some web framework stuff and only do the backend in lisp. The java is a killer feature for lisp adoption. A lot of companies use java heavily and being able to easily interface with that stuff is often a technical requirement and if not a technical one, a management requirement.