As someone who learned a little Lisp in the last few years, I think there is a good collection of books available for the newbie who wants to learn. For Common Lisp, Land of Lisp, Practical Common Lisp, and Ansi Common Lisp all seem good enough to get hacking quickly.

Thinking about community effects, I'm not as convinced a community represents a gating factor for hackers. I attend the occasional Clojure meetup (and Clojure/Conj for that matter). The meetups in my area are well-attended and run, although they could be improved with a better introduction and ice-breaker for more introverted attendees (yes, I've just outed my personality type).

But from an opportunity mindset, the Clojure community seems to have done an admirable job getting the message out. Multiple good books, the Clojure/conj, and a well-attended meetup in my area all make me feel like I may not only stretch myself and learn new programming techniques, but that I have some hope of advocating for Clojure in my workplace or, good grief, applying for an actual day job where I would use Clojure.

It's unclear to me that Common Lisp can offer that.