Not really an Apple guy, but I've had a Pebble watch for about six months now. Mostly it tells time using interesting watch faces, but when something interesting happens on my phone (appointment rolls around; email, text, or tweet arrives for me; weather alert is declared; GPS says there's a turn coming up; etc.) my watch vibrates and shows the notification.

Helpful, useful, fun...but not necessary. Also aggravating that I have to charge the battery every five to seven days.

"But whether the Constitution really be one thing, or another, this much is certain--that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist." --Lysander Spooner, 1867