Bought one today at the Apple Store. They didn't have them out yet but asked for it. I've been a Fuel Band user since April. I have a love/hate relationship with it because it's so damn inaccurate. I run 5 miles it tells me I only went 3. So that's my motivation for checking the Up out.
Can't comment of functionality yet, but not liking the design so far.
Aesthetically it's slimmer than the Fuel Band but a tad wider going outward. I'm not a fan of how the two end curl up at the end to grip your wrist. Nike's solution is a lot cleaner. The way the ends overhang means shirts and sweaters will get hung up on it and who knows what else.
Also for $129 -- just $30 less than the Fuel Band, you get no instant data readout or feedback. Everything has to be read from the App. That would not be a monster issue if it had wireless sync, but it doesn't (even though Jawbone is a BT speaker and headset co). So to find out where you are in the day you have to take the bracelet off, take the cap off, stick it in the headphone port, activate the app and sync. That's a lot of work just to find out where you are in the day. Even the Fitbit offers visual cues in the form of a growing flower.
So, so far not impressed. I'm going to reserve judgment until I've used it for a week but I don't think Jawbone learned as much about design of the Gen 1 as they think they did.
Please keep us updated and post any more opinions you have. I have a few more days to return my FuelBand and get an Up, if I deem it worth it. I really like the feature-set of the Up - the sleep tracking and vibrating alarms, especially - but I love that the FuelBand doubles as a watch and gives immediate feedback. BT syncing is just icing on the cake.
I'd love the additional features the Up has to offer, but I'm worried that the syncing method is going to really put a damper on the experience for me, especially as it's the only way to get feedback on how your day is going and if you need to take that extra lap around the block to meet your goal for the day.