You don't actually lose the metadata by commenting the code, thanks to git/svn/hg's blame feature, named identically in each. (I've not used darcs in a very long time, but it had something similar called "annotate".) If the code doesn't look like the comments say it is, you can check the timestamps and if that doesn't help, then you can crawl through old commits to see what's going on. It's useful enough that I've bound a key in my editor to display the blame'd code.
