I'm using a JawboneUP to track mood, steps, calories, and sleep. And the Withings Smart Body Analyzer to track weight, and heart rate. And a few open source gems to pull down the data: https://github.com/chocolit/dashboard
Different. Nike+ is more about exercise and sports motivation, Withings is more about the data. I feel inspired to workout with Nike+, Withings just gives me the data I want.