Matt Asay calls it a poison pill.
The Common Public Attribution License (CPAL) is based on the Mozilla Public License, but with two notable changes. First, the “ASP loophole” has been closed (good thing), which means that the source code must be distributed to users of the software even if it’s being run on a server (i.e. a web application). The other change is the “poison pill” — the “badgeware” attribution clause. This means that any other social networks that wish to implement the platform would have to give prominent credit to a rival, which sort of defeats the purpose of free software.
Matt Asay says:
If the point was to protect the Facebook platform from competition (i.e., derivative works), Facebook chose a good license. If it was to encourage development, it chose the wrong license.
The license has been approved by the OSI (though it doesn’t appear to be approved by the FSF), but “continues to be viewed with suspicion within the open-source community.”
Way to kill the buzz, Facebook.
(Bonus: Oh, and it’s not compatible with the GPL.)