I agree with others: practicing for the sake of practicing will almost certainly be boring. If you dont have an important real problem to solve, I find that the best way to make a learning task enjoyable is to make it social.
The easiest means for adding a social aspect to the learning process is to find people who are asking questions, and to try to answer them. Where do you find people asking questions? Others have suggested reading and replying to posts on PerlMonks, and that is certainly one such social avenue to try. Another option is to join a mailing list for a Perl project that you like. You could also join live discussions on irc.perl.org for projects or topics that interest you. (If you don't have an irc client, you can use mibbit.) Finally, exercism is a new option I just learned about, thanks to Gabor's Perl Weekly; a series of increasingly complex tasks are posed and individuals post their solutions for various languages; you can comment on others' solutions and update your solutions in response to feedback you get.