I think it really depends on how "new" you are. I've been programming in Perl for 4 years - and there is still much I don't know. So I would consider myself a new user of a particular function or feature of Perl rather than of the whole language. Not all Perl programming challenges may be that challenging to you, it depends on your background and previous experience.
I started with Learning Perl from O'Reilly. The challenges in the back of each chapter were just what I needed to get a toe hold in Perl. I started with almost zero knowledge of programming. If you already have some programming knowledge then I would recommend something more challenging (like trying to rewrite the Perl Cookbook). ;-)
