I've been looking into this myself.
Why are there no multi-thread Perl-centric application servers (ala Java's Tomcat) ?
mod_perl is not a realistic option for me because some of our customers use IIS / ISA proxy server.
What would be ideal is a standalone multi-thread webserver written in Perl that could be reverse-proxied using Apache or IIS/Proxy Server. I want to avoid the startup overhead of CGI, and the non-portability of mod_perl. Having a standalone HTTP app server that's proxied seems to be the way to build scalable web apps.
At least according to these guys...
The web is a pipe
fastcgi-scgi-and-apache-background-and-future
Is building a light-weight multi-threaded web-server in perl really that hard ?