mod_perl puts a Perl interpreter right inside the Apache Web server, so there's no wind-up time for any scripts, which stay compiled between hits. For a site which uses a lot of scripting, especially when tied into a database, upgrading to mod_perl can be a life-saver.

It takes a bit of work to get CGI scripts running properly with mod_perl, but it is a lot easier than using FastCGI, re-writing everything in C, or buying more servers. If you're already using "strict", then the changes you have to make are pretty minor. If your code is wild and wily, a good house-cleaning effort is advised. The only reason is because global variables stay initialized between Web hits, which can have the interesting effect of adding your items to someone else's shopping cart, for example, because the shopping cart structure wasn't initialized for each "hit".

mod_perl like methamphetamines for your server, only without the nasty coming down part.