Shawn Blanc does a great review:
It is clear to me that the UP is not a workout tracker as much as it is a low-level activity monitor. Or, put another way, I’d say the UP is an easy-to-use tool to help you become more aware of your own activity.
The UP would die on my wrist.
I picked one of these up last Friday at the Apple Store in Burlington, ON and have to say I’m quite happy with it. The vibration alarm is really nice and wakes me up but not the wife, and I think overall it’s a good value since it helps make you more aware of your own activity levels and will likely motivate you to move a bit more. I know I’m moving a lot more than I did previously.