My impression of Lisp/Scheme, and the reason I've never really learned them despite an interest in the paradigm, is that the fundamentals are easy enough but once you want to venture beyond them (into, say, multimedia or web programming) you run into a morass of outdated and poorly documented libraries that are unusable or inaccessible for inexperienced programmers. The "do it yourself" culture and an implicit assumption that everyone knows C seems to result in most bindings being really flaky things, compared to the well-documented, high quality libraries for imperative scripting languages like Python and Ruby.

Things seem to be improving in recent years- ltk and lispbuilder have documentation that doesn't completely suck- but the problem still exists, especially for Scheme.