I especially liked the comment about going back to your own code 5 years on. Back in the late 60's I started working in Fortran-IV. This same code is the root of a product which has been through many incarnations in a variety of languages over more than 30 years. Incarnation TWO was a problem, there were no comments in incarnation ONE so I had to go back and work it all out by hand. But since then, each change or addition in whatever language has been thoroughly documented, to the point where the comments are now about 1.5 times the size of the code itself and they provide a wonderful insight into over thirty years of development.
in reply to Reasons for looking at your favourite module's source
A simple rule:
If you comment well, no amount of comment is too much
And yes, there are Perl coders out here who have been at it that long!