A few dozen Up fitness band owners are complaining of "bricked" devices in the Jawbone user forums. Some owners are even complaining that their second and third replacement units have bricked. The most common symptom is a failure of the device to turn on even after leaving it on the charger for hours at a time. Reseting the device, by holding the Up's button down while plugging it in to the USB charger, doesn't bring it back to life.
For what it's worth, my Up review unit maintained its initial charge for 10 full days, exactly as Jawbone said it would. I then recharged the unit for a few hours (Jawbone says it'll recharge in 80 minutes) and it died three days later, causing me to oversleep this morning when the Smart Alarm failed to vibrate me awake. I have not seen the band become unresponsive, however, and it's too early to tell if I'm having a battery issue. Having said that, I did charge the band to 100 percent today and it's showing a 71 percent charge now just a few hours later.
Update 16-Nov: My Up does seem to be suffering a "capping effect" after charging, only holding charge for about 24 hours. It's also showing inexplicable and random gaps in data collection after syncing. Although it's not bricked, I've lost all confidence that the device is properly functioning.
Jawbone is offering free replacement bands and pre-paid packages to return the defective units on Jawbone's dime. While the company has not identified the cause of the issue yet, we have received a statement saying Jawbone is aware of the problem and is "working closely with users to identify the issues and fix them."