Just to add onto what tachyon said ...

mod_perl can be much more than just a CGI accelerator. The mod_perl API gives you access to the various phases of the Apache request cycle as well as some of the internals of Apache itself. Using mod_perl "handlers" you can program in a way totally different from regular "CGI scripts", and more akin to Java servlets. Of course the deeper you get the more of your foot/leg/lower-portion-of-body you can shot off if you are not careful. But as they say "with great power comes great responsibility". If you are really interested, I would recommend the O'Reilly Eagle book, it gives a better "tutorial" style introduction than the online docs IMHO, and then the Mod Perl Cookbook if you really wanna get into it.

I mention this because seeing "mod_perl" in a job opening may mean this kind of mod_perl and not just "running CGI scripts in the mod_perl environment". They are really 2 different worlds (again IMO).

Good luck.

-stvn