I'll second the mod_perl Guide (http://perl.apache.org/guide). Stas et al. has worked long and hard to put together this very comprehensive document. No, it is not short. But if you read the guide, along with the Eagle book "Writing Apache Modules w/ Perl and C", you will be able to do all the common tasks a mod_perl programmer might be asked to do. And you'll at least know where to start for the uncommon requests.

There is also the Mod_perl Cookbook coming out in January http://www.modperlcookbook.com/. I gather the format is similar to the Perl Cookbook, which is most helpful if you have a specific task you would like to complete.