I would add to this:

Delete unused code when it is released or goes into production.

There's some very good, valid reasons for leaving in comments in non-production/unreleased code. I find myself trying different things, adding/moving code around, and I comment as I go. Sometimes, I'll have a 1.1 cut of test code sitting inside a 1.0 version as I play around with it.

Your comment about using cvs rings true to me, and I'm a firm believer in it, but only again, in released code should you prune. If I'm working on a file, and it's going through several milestone stages working up to a release, I don't want to have to remove comments or commented code, check it in, then have others work on it, check it back out, copy back in the code from the first imported version, hack it up, take out the comments, commit it back, etc.