If I was still playing WoW I'd be somewhat pissed off at the idea.
I was quite a regular forum poster on our realm forums, and would pretty much be forced into stopping by this change. The whole using it in game to add friends is ridiculous too, or at least the fact that it makes you visible to friends of friends and reveals all of your characters to the people you add. But you can avoid that and just use the old avatar name method.
But at the end of the day, Blizzard are going to get the response they're after (less shit posts via less posts on the whole as people begin to shun blizzard forums in favour of other sites, BB over on EJ has always had superior content anyway for a very minimal fee).
As of yet, I've not felt the need to use the SC forums, and doubt I ever will.
and SC is much more of a loners game, doubt I'll feel the needs to add many friends to that

ps: Sarras, you can come troll me any time

Oh, and a word on possible exploits, people already have macros to exploit it through addons (as blizz kindly included API functions for the real id friends lists), and a Blizzard staffer put his name up on the forum and harassment ensued. Roll on 4chan style witch hunts on the blizz forums.