Why should PPRuNe worry? The result of this case is that the individual concerned is responsible - a good thing, in my humble opinion.
FriendsReunited pulled the comments once a complaint was made and were
not taken to court (note the difference from the
Demon Internet case of a few years ago - Demon did not remove defamatory comments on newsgroups they hosted once requested to do so). Presumably PPRuNe must just assist in deleting disputed comments and take reasonable steps to identify the sender (i.e. IP address and registration details) when and if requested?