Saying they'll quit.
Now, don't get me wrong. I fully support your decision to quit over something like this, or even just because you woke up and didn't have any clean underwear. It's your subscription fee, and if this change means you won't be buying another Blizzard/Activision product ever again - good on ya mate. Voting with your wallet is one of the most powerful tools you have in a capitalist world. Don't buy the product. Don't support them, stop talking about them, just pretend they never existed (after all, even bad press is free press).
Don't limit yourself to just Blizzard games, since you can bet this wouldn't have happened without Activision's support/approval. It won't be long before your Call of Duty and Guitar Hero profiles will be linked to your real name as well.
Go big or go home
Here's the final thing though. Saying you're canceling your account and then logging in to put a few more levels on your alt, or get in on another guild run, is just you talking loud. You're still putting forth effort into toons and enjoying the game. Your quitting is probably about as likely to stick as me swearing off coffee. It's just not gonna happen.
No, if you want to really drive your point home, you need to do the following.
- Cancel your account - give the specific reason of RealID as to why you're quitting.
- Never log in again - even to say goodbye.
- Delete your toons. Don't give your stuff away - delete them. Giving your stuff away only supports those that are sticking around.
- Email privacy@Blizzard.com and ask them to remove all personal information about yourself from their database.
- Mail your authenticator back to Blizzard (if you have a keychain one) in little pieces - with the Serial Number scraped off, otherwise completely remove your authenticator from your phone. If you don't have one, even better - get one, attach it to your account, and THEN remove it.
- Destroy your disks, lose your game codes, and change your password to something completely random. For added strength, create a dummy email, change your account email to THAT address, and THEN change your password. You want to completely remove any hope of getting the account back.
A less dramatic path
Don't take this the wrong way though. I'm all for speaking out against something if you don't like it. Post constructively on either the US or EU thread about RealID. Send emails to Blizzard expressing your concerns, or pick up the phone and call them (enjoy that hold music). Open tickets in game, participate in rational discussion, and remember that this is a game.
***Edit - as Failadin mentioned, disable RealID in the parental controls. That will get their attention more than anything if suddenly a million subscribers do that.
I agree that we don't know where this is going. First it was your name with RealID for some friends, then required to post on the forums. To me this is neither a reason to quit, or a reason to boycott all things Blizzard/Activision. Now, if I'm suddenly required to have my real name tagged to my Armory, and required to have it linked to a Facebook page - different story. For now I'll keep a weather eye on what's happening, and I'll continue to enjoy this for what it is - a game.
Protest any way you want, it's your subscription fee. Just don't get all high and mighty about canceling your account, and then come back when either a) this is changed, or b) you decide you really can live with not posting on the forums while you get your Cata fix on. I can't stand people that go half way in something.