Comment by iib

Eric S. Raymond is against them, but also argues that they are harmful--as opposed to just useless--because if they ever got to court, a jurist would look at the practices of the community to decide whether such a thing is common enough that they should be required. [1]

I know GNU does it (at least for Emacs) under the reason that the FSF can go after any GPL violation only if it is the clear copyright holder, but no such case exists, to my knowledge.

[1] http://esr.ibiblio.org/?p=8287