I have a Pebble -- until recently, a Kickstarter-edition one, though it malfunctioned and the company quite helpfully replaced it.
I originally got it as a geek toy, a whim, but it turned out to be hugely useful for me, given my constraints and work circumstances. Largely, this came down to three factors:
I manage people, and at least at my current company that means that the vast majority of my time is spent in meetings. Having a Pebble on which to see what messages I'm receiving (just for text messages, not FB or email) means I can know when someone's texted me (a rare, but potentially important, occasion) and be able to see what I got without having to reach for my phone in my pocket; it also means that because being able to see the message doesn't necessitate using the tool with which I respond, that I'm less likely to respond immediately, which makes the process less disruptive to the people I'm in meetings with;
I used to miss meetings often because I'd get in the middle of something (or another meeting) and forget to check where I next need to go. My phone quickly vibrating in my pocket was easy to miss. But my watch vibrating? For me, it's unmissable, and it makes me much more aware of where I need to go next.
The other factor that's made a huge difference is not work-related. Being able to control music on my phone via my watch is a trivial improvement when I work out, but it's made another issue basically go away: The "What the hell did I do with my phone?" problem. If I can't find my phone these days, calling it doesn't necessarily work -- it's typically in quiet mode -- but using my Pebble to get some music playing on it, and increasing the volume, is usually immediately helpful in figuring out where the phone is.
You could, of course, argue that these three factors are not, or should not, be relevant to the average geek -- maybe you don't have as many meetings, or are more disciplined about checking your calendar. And God knows we all found our phones before we could remotely start them playing music. But it's been very helpful to me.