That last bit is always the rub, no? If something is largely pre-implemented (via CPAN, etc.) in Perl and Perl will perform adequately, I tend to use it. If I'm going to need to write a lot of my own code I tend to use Lisp. Fortunately more and more useful stuff is becoming available in Lisp all the time, e.g. at Cliki. Anywhere near CPAN? No. But often enough to push the amount of stuff I need to do on my own down enough to where I can use Lisp.