I use http://beeminder.com/ http://beeminder.com/ for this. For my weight, I have a Fitbit Aria scale -- I weigh in daily, it uploads my weight to Fitbit and th

I use http://beeminder.com/ http://beeminder.com/ for this. For my weight, I have a Fitbit Aria scale -- I weigh in daily, it uploads my weight to Fitbit and the data is pulled in by Beeminder. So there's no friction in getting data into the service (I just blearily step onto the scale every day) and there's no way for me to lie, even if the thought of financial loss tempted me to.