Cliff Kuang on the Jawbone UP:

As is, the UP introduces just enough friction into the process that it never quite melds into your routines. Simply having to take the wristband off, uncap the end piece, plug it into your phone, load up the UP app, and then have it synch means that it becomes another chore–rather than a new feature of your constant dialogue with your smartphone.

This is a really great take. I am currently testing out the Fitbit (which he also mentions) and find that he hits on a lot of problems that I see in both devices — mostly that it has certain friction points that make it less interactive than it needs to be.