I'm not sure if you found this one yet, but this article by Tom Christiansen is a great reference on perl prototypes and how they can go wrong. (IMHOP, prototypes are a horrible hack and I can't imagine a case where I would use them at all.)
Good article. Thanks. The only time I've ever wanted to use them is to get the ability to pass a sub reference in as a bare block, ala grep, sort, map, etc. Tom's article leaves them for another time but it's good nonetheless.