In the first phase we will be able to build Glances, Actionable Notifications and iPhone powered apps. The last of which has me most excited.
Apple took a clever approach to handling the extremely constrained power environment of the Watch (at least initially). To start with 3rd Party apps will run in a split mode. The Watch itself handling the UI parts of the app with an iPhone based app extension doing all the heavy lifting and computation. This is architected in such a way as to enhance interactivity (it isn’t just a streamed movie) while still keeping the Watch components very lightweight.
I reckon that somewhere between 25% and 33% of all my interactions with my phone could be categorised as Glances or Actionable notifications. What's the next thing in my calendar? What's the next item on my Things to do list? What was that SMS? Pause the Downcast player. etc. etc.
In the new post watch world, 1/3 of the time, my phone stays in my pocket.
Also, great new income stream for the developers of all our favourite apps.