Your friend who plays Hearthstone is about to pester you again about why you don't play the game, so you might as well know why. Blizzard has released a new Shaman character, Morgl The Oracle, who can only be unlocked by referring a friend to the game...
This isn't a "well I'll just get my friend to install and grab my hero" deal either. Your friend has to create an account and play Hearthstone until their heroes combined levels reach 20. In the short term, you'll get a classic card pack for each friend you recruit for up to 4 recruits so that's nice if nothing else.
Other than that, Blizzard also announced some slight cosmetic changes with their latest update. You can read all about them in their official patch notes right here.