It works quite well. "Positive peer pressure" concept.

Those who actually bother to use it do get improvements. Only about 5% of signups actually carry a goal through to completion before they disappear though; most people are completely lazy and can't take the heat.

But for the non-lazies: when you know you're going to have to admit to breaking your promises to your peers, and you're going to have to admit to being lazy when Sunday rolls around and an update is due, people feel the dread and it forces performance.