I use my Pebble watch mainly for running, as it allows me to keep track of my distance, time, and pace just by looking at my wrist without having to go through hassle of taking out and fiddling with my handphone.
To do this, you need to have a Runkeeper account (basic membership is free), a bluetooth enabled smartphone (I use the Iphone), and of course the Pebble watch.
This is how the interface with Runkeeper looks like.
Pebble watch allows control of music from the watch as well. However, as I do not run with music, I do not have much use of this music function.