Blizzard is going to make Battle.net mandatory. To make the change less "painful", they are trying to lure people into going willingly by offering a Battle-Bot, in league with Mountain Dew.
You use your email address to make a Battle.net account. You merge your WoW account into the Battle.net account - this uses your email address/pword from Battle.net for your WoW account at that point. Then you can claim the Battle-Bot. A key is mailed to your characters - all of them - from Jepetto in Dalaran. If you make a new character, they get a key too.
This, I suspect, is to set Blizzard up to host other online games. Can we say Starcraft or Diablo?
Anyway... You can also gain tokens to put into drawings for "l33t" gear.