Really you can have overcommented code. I have worked for a company where the policy was not to remove anything from a file but comment it out. A bit like keeping a revision history in the file itself. After a few years code rot sets in and productivity slows down.
The gripe I have against these //CDC (I thought it stood for Cult of the Dead Cow ) comments is that they add no understanding to the code. It really does not matter who added the code. If I wanted to know that there is a good CVS function that can tell me that (annotate).
Comments should ideally add the reasons why something it is done, much less what is done (you can see that for yourself by reading the code). Marking different sections is nice too, especially if you have long blocks, a comment what the block was about helps a lot IMHO. "///CDC tag" is neither of those things. It may be handy in between commits, but they have no meaning for anybody else (apart from telling 'CDC was here")
Sure those //CDC comments could be removed, it is defenitly not the end of the world, but it is still work that could have been avoided.