As some other people have said, it's a tool, for some jobs it's the only tool, for others it's very much the wrong tool, and in most cases, it's one of many options.
in reply to How do you feel about mod_perl?
Professionally (meaning that they pay me, not that my code looks professional) I've tended to not to install it, because they tend to be shared hosting systems, system load doesn't tend to be a problem, and most users wouldn't touch it. The caveats about how you can do a fairly good job of locking up apache with it, if you do things incorrectly didn't make it seem a good candidate.
OTOH I recently came across the sort of thing which mod_perl is ideally suited to - basically a high-traffic server where every hit requires a database hit. By caching the script (for 99% of hits were on that one object) and more importantly, by not having to set up and tear down a DB connection millions of times a day teh efficiency gains are tremendous. The server simply couldn't cope running apache and mysql on top of the rest of its functions without mod_perl, whereas with the script modified to use it, there's plenty of headroom. The clock ticks saved by not having the setup costs for each hit meant that each request finished faster, keeping the number of apache and mysql threads down, gaining more efficiency from that.