I backed the Pebble Kickstarter project on day 3 and was anxious for all 471 days of my wait. There are pros and cons with it, I find myself wearing it for a month or so, then not for the next 3 weeks. Torn in between the two worlds. Plenty of reviews have been written, so I'll skip that.
I found one shocking side effect of wearing the watch that I had not expected, and it remains one of the largest sticking points for me. It isn't the Pebble's fault though.
Volumes have been written about how nice it is to leave your phone in your pocket. While this is true, it does mean you are potentially looking at your watch as many times as you were looking at your phone. There is a social understanding (to some degree) that looking at your phone is accepted. Yes, it is rude when you're with people, but a quick check here and there is usually acceptable (highly dependent on the situation and company of course).
When you're with those people and checking your watch, you look like you're counting the minutes until they're done talking or until you can leave. It comes across as immeasurably rude, and I've gotten the reactions to support that. I find myself having to awkwardly explain that I'm not looking at the time, but rather a push alert of some kind. If you're getting push alerts as often as me, you really just appear to be rude, impatient, and selfish should you chose to check your watch each time. Most of us don't look at every alert right when it comes in, but when your wrist buzzes it quickly becomes habit to glance quickly.
As with any technology, it is the responsibility of the user to exercise common courtesy and logic. This isn't a slam on the Pebble. It is, however, a side effect I did not consider beforehand.