If you have the new camel (3rd Ed.) Chapter 12 gives a fair overview if you understand OO and perl but haven't put the two together yet.

The already mentioned Object Oriented Perl by Damien Conway is, in my humble opinion, the best way to go. As it not only walks you through the pro's and con's of different object constructs but, for this reader, openned up a new way of looking at perl itself in it's 2nd Chapter

As for the O'Rielly Advanced Perl Programming, I have a hard time recommending that particular book to any one but 'C' programmers and even then with some reluctance as it's almost apologetic treatment of perl & OO-perl makes a person feel like they are just practicing an exersize in OO rather than learning to exploit and explore perl Objects.

Going through my bookmarks I found this reference Steve's OO perl Page but I haven't checked it out yet.