I was gifted a vivofit recently for Christmas and I absolutely LOVE IT! I'm also ordering a heart rate monitor to pair with it, but it's a nifty product and has gotten me to keep on track with my fitness. It pairs with multiple apps (I use MyFitnessPal and Under Armor Record) to keep you going and watch your progress. So far, on one week, I've dropped 2 lbs. You can monitor multiple things on it: Steps, your step Goal, Miles Walked, Calories Burned (both active and resting), Date/Time, and Heart Rate if you have a monitor for it. I use it paired with the Garmin Connect app it syncs with to track sleep as well (if you hold the button long enough for it to prompt "SLEEP", it will register the time up until you press the button again as sleep mode in the app).
All in all, great product, helps you stay on track, BUT it is app-dependent..