in reply to How common is mod_perl?
However, I think HTML::Mason doesn't really require much mod_perl knowledge. It would help you understand what's going on underneath, but you could learn HTML::Mason at a more conceptual level if you wanted. If the main reason you wouldn't learn HTML::Mason is because you're intimidated by mod_perl, I think you can eliminate that reason. The hardest part of HTML::Mason when I first learned it was the initial Apache configuration, but it's well documented and there's a mailing list to read archives or ask questions.
Typically with HTML::Mason, you put HTML at the top of a template page and some Perl at the bottom. The HTML will have special tags in it, similar to JSP or ASP. Then below it, you'll put some Perl code to initialize variables. But I think the powerful thing about HTML::Mason is its "object-orientedness". You can use "autohandlers" to automatically produce parts of the pages, and you can use "methods" that are object-oriented so you can override them and whatnot. I guess in the end it might be just what fits best with your style, so maybe HTML::Template or Template Toolkit makes more sense for you. But knowing mod_perl will still be useful anyway.