[jacquesm]

I think a bigger factor is the amount of prior knowledge required before you can be productive.

In C (and c-like languages) that barrier is relatively low, a handful of concepts and a very limited subset of library modules and you can go a long long way.

[gaius]

Indeed. Lisp programmers with 20 years experience are more productive than Java programmers with 2 years experience. That doesn't say anything about Lisp vs Java (or, not nearly as much as some would claim it does).