OpenPGPComment is a WordPress plugin that allows you to display signed comments properly. Users can sign their comments with gpg, and the server then displays these comments without the signature in the post comments, but offers a popup window with the gpg output as a link. Nice idea.
Digitally signed comments are not only useful for associating comments with users - they also offer advantages for the user themselves. Specifically, it is ensured that signed comments have not been subsequently altered by the server operator. A not insignificant advantage, especially in weblogs, where the server owner usually has significantly more options available.
I would have liked to try it out myself, but it requires proc open - and proc open is only available from PHP 4.3 onwards. And in Debian Woody, there is still a PHP 4.1.2 ...