Plenty of reasons to.

sed, awk and Perl practically don't have any competitors in their stride.

When you learn those tools, you basically realize that all the while you were using a hammer, while what you should been using is a screw driver.

I'm planning to learn Perl for a combination of its ubiquity, the cheap O'Reillys I came across recently, and contrarianism. Kamaal's answer also covers it really well.