Once, doing maintenance, I had to find and fix a bug in some code. I spent ages sifting through a printout of the source trying to figure out how it worked and what was going wrong. It was only when I loaded the source into a syntax hilighting editor that I realised that a big chunk of the code I was trying to decipher had actually been commented out.

Production code should not have any commented out sections. Production code should *always* go through some sort of version control system while it is being developed. This means that all changes made during development are recorded, but the poor maintainer does not have to see them unless he needs to.