I don't know if anyone here is a Hearthstone fan, but I was doing a little snooping around the installation directory and found some interesting files.
In the Hearthstone/Data/Win folder you can clearly see that the game was made using Unity, this in itself made me smile. But upon further inspection, if you head to the Hearthstone/Hearthstone_Data/Managed folder you will find something even more interesting... PlayMaker.dll!!!
It's not really clear what this means, or how and what exactly they are using Playmaker for. But it's very exciting to see that a huge player such as Blizzard has realized the enormous potential of these tools, and is using them in a AAA production.