mod_perl really gives you some power that no other web servers offer right now. I see all other web servers eventually moving towards a model similar to mod_perl, if they're smart -- but none have done it yet.

So, I say learn HTML::Mason. Okay, mod_perl is difficult. There's not a lot of documentation that will spell everything out for you letter by letter. But when you're done, it'll give you a very marketable skill and a deeper knowledge of what web servers are capable of.

Besides... once Apache 2.0 gets stable and becomes mainstream, who'd be stupid enough to run anything else? :)

I've only gotten a small taste of what mod_perl can do. If anyone has some really great documentation links, please post here. Thanks! (All my good mod_perl links are in my bookmarks at work.. I'll post mine here tomorrow AM EST.)