Last night after watching the keynote I actually did want one, after not being at all bothered initially. But 24 hours later I think I've regained my sanity and once again, other than the "oho shiny", I really can't see the point of it.
The point of the Watch ultimately is to get the information that's pushed to your iOS/OSX devices (messages, directions, social media b******s) delivered to you in a way that's more immediate when out and about.
So for instance when I'm commuting to work in London, if my phone goes off in my pocket, like most people I'm compelled to look but physically taking it out can be a faff due to being squashed on the train or in a busy street/station and/or being in a warm/longer coat and layers and it being buried.
The idea that I could just glance at my wrist instead might seem silly but if it genuinely makes the process of communicating or performing an action more efficient and saves time, that's a win in my book - after all, tech should be there to make things easier/more efficient/more transparent.
Also other stuff like:
If I'm using the map to give me directions somewhere when walking, instead of going down the street glued to my screen, which can be either hazardous or unsafe depending on location, I can simply rely on the Watch's Taptic Feedback to tell me to take the left/right etc.
It's more subtle with messaging etc than getting your phone out, which is handy in social/business situations when it might appear rude.
You'll physically feel all notifications, unlike a phone where you sometimes miss texts etc because you failed to feel the phone vibrating in your pocket or didn't hear a call because it was in your bag. No more irritating ring/text tones, just the alarm (which needs to be annoying to get me out of bed to turn it off).
The question I guess is whether the above (and whatever else they come up with for it) is worth £299+ of your money.