I couldn't really tell you from a technical standpoint. Perl has always been capable of doing what I needed it to. Some of these other folks with more demanding needs have already pointed out technical aspects of when not to use Perl.

My focus is usually a cultural aspect. Since I tend to do more contracting work, I have to look at the environment when I decide what would be "the right tool for the job". If the company has some reasonably skilled Perl folks, or it's most likely that I will be the one maintaining the project, I feel safe using Perl. If it's a bunch of Java people, though, I would lean towards using Python. It would take less work for them to stretch their brains around Python's capabilities than if I threw a few Perl modules at them.

Occasionally, when I just want to have some fun, I use Ruby. Because I can.

Still, I'd say Perl is the best tool for the job around three or four out of five times. The majority of the time, but nowhere near all the time. You just have to look at what you need, and who else will be looking at your code.

"All you need is ignorance and confidence; then success is sure."-- Mark Twain