Perl and Apache make a powerful and popular combination. There are several projects that use these two technologies.
The Mason project embeds Perl in HTML with a reusable component model approach. It allows caching, templating, etc.
mod_perl is one of the most veteran and successful Apache projects. It embeds a Perl interpreter in Apache and allows access to the web server internals from Perl. This allows for entire modules to be written in Perl or a mixture of Perl and C code. In the 1.3 Apache versions, one interpreter has to be embedded in each child, since the server is multiprocess based. In heavy traffic dynamic sites, the increased size could make a difference. Apache 2.0 is multithreaded, as recent versions of Perl are. The next generation of mod_perl takes advantage of this and allows for sharing of code, data and session state among interpreters. This results in a faster, leaner solution.
Make sure you also check axkit