If you ever expect to work in a unix environment you'll be glad you know perl. even if you end up using it only for "shell scripts on steroids" it certainly won't be a waste of time. Java, PHP & C aren't exactly the best tools for automating/glueing tools on unix. Perl is.

As for "non-trivial" "real" projects, this year I've made most of my money working on a 99% Perl project. The other 1 percent of the project was done in C/C++/XS (mainly glue to existing libraries, but also some code to increase performance). The year before I made most of my money coding Java. Next year I expect at least some Ruby/Rails projects.

Every decent language will teach you something valuable as a programmer. I'm glad I know C, C++, Perl, Ruby & Java. Working with different languages keeps your brain open to new ideas. Also, you'll be more likely to choose the right language(s) for the job.

In other words: do Perl AND some other languages. I would recommend you also start with C. Perl & C are a pretty good match if you want to combine them and C is everywhere. Writing C will also make you appreciate all the work Perl does for you :-)