Undecided. I almost never wear watches, but I would wear one for the HRM/activity tracking feature instead of using a Fitbit, Polar HRM or whatever. Being able to see messages/calls etc. without having to pick the phone up or take it out of my pocket would be convenient. I don't see where a lot of other apps are practical on a screen that size, though. Maps, mail, calendar and a lot of others would be basically useless on a tiny watch screen.
Some have listed it as a disadvantage that you have to have a phone nearby to use it. To me, that's a big plus because if they built a cellular radio into it and made it an independent device, it would be one more device that would have to be added to a cellular plan and entail monthly connect charges (not to mention it would be bulbously huge on your wrist). If Apple had done that, I'd definitely be 100% on the 'no' side because I'm not buying the watch, then paying another $15-25 monthly for it to do what my phone already does - especially since I almost always have my phone with (or near) me anyway.
I'd also like to know more about the water resistance/proof specs - or lack thereof. If it can't get wet, I'm out. All in all, there are still too many unknowns (price, specs, etc.) for me to make a decision yet.