I have one and it's quite a nice device. I'm currently using it to monitor my sleep pattern. (If you have Windows mobile change your region to the U.S. to initially get the Microsoft Health App - Purple app not the red one then change back to the U.K.)
Got mine on Saturday from my mate. Very happy with it! Got a large, which i have on the 2nd to tightest notch, so would have been happier with a medium maybe.
No screen protector, so wore it all weekend without and it has picked up some micro scratches around the bezel [not the actual screen]. Got 1 on the way from the Usa via Amazon - so not wearing it to work today as know it will get desk warrior scratches!!!
Liking it so far. Need to get it set up right for notifications though as seem to get all sorts through. Did like that it pinged up when Leeds Utd scored against Derby though.............. Tracked my sleep and that's interesting as well as a very slow walk with the family yesterday. 1.9 miles took us just under 2 hours! [hot chocolate and duck feeding stops en route]
Think version 2 of this could be cracking - and i hope this version gets well developed for now it's out. And not just for iphone/android users of it.
I'm loving mine so far, not had a chance to really put it through it's paces at the gym due to work, but the functionally is great.
It does take a little bit of getting used too as it is quite rigid, and it tracks steps and calories more conservatively than my Fitbit which seems to be due to the added benefit of the heart rate monitor.
I cant wait until Microsoft releases the full functionality of MS Heath including the web interface and the full range of the Band's sensors.