I expect at least a few people here have heard about this - it's Blizzard's latest game, a free card game in which you can build a deck based around any of nine characters, putting various spell and creature cards into your deck. Then you go up against other players (AI or actual people) in order to try and defeat them (by whittling down the 30hp belonging to that character). The game itself is free but you can pay to get extra cards earlier - all cards can be bought with gold, though, which you can get by winning games and stuff. You just get them quicker if you pay real money.
Hearthstone is currently in Closed Beta, but you can opt in for a Beta key if you have a Battle.net account. I opted in but wasn't really expecting to get a key. Then someone on another forum said that Blizzard had randomly sent them about ten and was giving them away to anyone who was interested. So I got a key that way, installed the game, started playing it...and then about a week later had a random e-mail from Blizzard saying "Welcome to Hearthstone!". I thought that was a bit weird, because I figured if I was gonna get a welcoming e-mail, it'd be when I first set the game up. But no, it turned out they'd finally decided to send me a Beta key...which I no longer need.
So does anyone here want it? :D