As an extension on chromatic's idea for a Perl Golf contest; perhaps just a contest with a bunch of different "prizes". Post a problem and ask for, eg.:

• the fastest solution
• the shortest solution (Perl Golf)
• the most extensible solution?
• most Perlish solution (sort of like Perl Golf, considering the nature of Perl :)

and so on. You could attach different amounts of XP points to the different prizes, or you could make the points all the same.

An example of a question might be along the lines of, but perhaps more complicated than:

• Given a sentence, write code to reverse the words in the sentence.
  (join ' ', reverse split / /, $sentence)

Another example might be the recent post on the madlibs implementation, which was a really good starting point and, I thought, contributed to some really nice ideas and code. Something along those lines, basically. Just a thought.