This is going to really enable some interesting apps. If anyone has been on the fence about buying the Band, the recent updates have been really great, and this should make it even better going forward.
More info here.
Additional functionality includes the ability to:
Build apps that support Windows.
Create your own custom layouts for pages on third-party tiles using icons, text, buttons, and barcodes for payment options.
Receive events and button-click callbacks from the Microsoft Band to your phone app. If you press a button on a page inside your tile, your app would know which button was pressed.
Connect to the Band from background tasks.
Tap into calorie subscription from the Microsoft Band.