From where I'm sitting (with the names of several Ruby extremists in my phonebook), I know that the things that grabbed them were standard libraries that they liked, including easy RMI and network usage. By contrast, there is no single free lisp distribution that comes with a comprehensive, well-documented, and easy-to-use set of libraries, as well as an easy way to upgrade them, preferably involving untarring, and none of the fragility of ASDF.

Quite apart from that, we don't have a single killer library, like Rails was for Ruby.

"After all the flurry of enthusiasm and activity following the ReddIt rewrite, we got flooded by a grand total of, huh, 1 (one) user, besides Marc and me, who contributed a couple of entries (thanks!)."

Source: http://www.paoloamoroso.it/log/060105.html

PCL provided some wakeup for lots of people that didn't have Lisp on their radar. I wonder what the retention rate has been.