In our review of the Pebble SmartWatch, we only had two complaints about the software: a lack of apps, and a lack of utility. The second point stems from the fact that the Pebble can only receive alerts from your phone, and it can't send information back. Both issues have now been addressed by the Pebble SDK. Developers have been cranking away on watch apps for some time, but the latest SDK update adds AppMessage, a method of implementing bi-directional communication for Pebble. Translation: your watch can now tell your phone to do stuff.
Of course, support for this feature will require Android app developers to either bake it into their existing apps, or create a bridge application, plus the official Pebble app. But theoretically the sky is the limit here: a watch app could change basic functions like enabling/disabling WiFi or silent mode, select from a batch of pre-made SMS or email replies, feed your Digimon, et cetera. I'm most excited about the possibility of extending widgets to the Pebble, so I can turn on WiFi tethering without pulling out my phone.
At present, the SDK only supports two-way communication with one Pebble app at a time. If you're wondering where all these interesting apps are (since the official Pebble app only includes some nerdy watch faces) check out AllPebble.com or its alternatives. Apps that take advantage of these new software goodies should be popping up soon. Developers, head to developer.getpebble.com for all the tools you'll need - the new stuff is explained here.