Dan Weinreb posted common Complaints About Common Lisp. My personal complaint is in there — the lack of libraries that are well-documented and regularly updated. I think it’s a critical mass problem: so few people are using Common Lisp in their day-to-day work that there’s not enough momentum to keep the libraries going and make them fool-proof. Too many Common Lisp libraries are weekend projects that never make it out of alpha.
I’m guilty of the same offense: my one and only (very small) Common Lisp library — a bridge to run an embedded Perl 5 interpreter from Common Lisp — went a year before I heard from one lone user. By that time I had switched to Ruby.
The test of a really good library is not that it’s there, but that you don’t notice it’s there. If I want to scrape some HTML in Ruby, I don’t need to think about it, I just type “require ‘hpricot’” and it works. If I have a problem, odds are someone else has had the same problem and Google will find it. With Common Lisp, one can feel like a lone voice crying out in the wilderness. There’s a bit of a frontier mentality, too: “Well, if it’s broke, fix it yourself, citizen.”