My brother has one.
I had a glance at it a couple of weeks ago. Some elements of it are very clever, and have their uses (the fitness app removes the need for a separate device like a FitBit, Jawbone, Nike thing etc for example) . There aren't enough useful features to make me want to go out and spend a few hundred quid on it though. The user interface isn't nearly as friendly as an iPhone- he would agree with this- and a number of functions we take for granted on the phone are a bit of a pain in the arse on the watch. It tells him to get off his backside and stand up regularly too, as part of the fitness app thing. Which he says is annoying. I guess there is probably a way to turn that off though. Battery life seems to be alright, contrary to popular expectation, primarily as you're not really fiddling with it all day like you might with a phone.
He's acquired his through his job and his opinion of it is that, while he quite likes it, he wouldn't go out and buy one himself.
I've got a wife who does this for free.