To those who, like me, won't be able to attend TPC 2001: Simon Cozens has published the text of his Perl 5 Internals course notes. The available formats and PDF and Postscript, although he indicates you can get the original sources by sending email.
I downloaded it a short while ago, and I've found it fascinating reading, even though I'm not planning on hacking on Perl 5 source (not before I read this, anyway ;-) Personally, I think this will go a long way in improving my (and anyone else's) Perl programming skills, as well as cluing me in more on the discussions on Perl 6.
You need at least a reading knowledge of C, although in some cases, code is "illustrated" with a Perl equivalent.
Grab it. Read it. Give it to your best friends.
/me gets off the soapbox.