Writing your WebApp in Lisp or another trendy languages like Scala, Clojure, Erlang, etc. is a nice story for viral marketing, because the communities around those languages are desperatly looking for "killer applications" and "success stories". That's a lesson i learned from reddit.

True, but this only works if you then switch to Python and get all the Lisp/Scala/Clojure/Erlang programmers' knickers in a bunch. (I'm not English, by the way; it's just that the Brits have a gift for odd metaphors.)