(I'm worried that I'm turning the comments into Beeminder Evangelism Hour here but I can't seem to help myself. I guess Hacker News of all places will be forgiving of that...)
Myself, I've been using Beeminder many years ago for a while. It significantly contributed to my stress and misery back then, as I lost money to it in a crucial time where I didn't have much of it, and my goals were very much related to improving my financial situation :). But that's not counter-evangelism! To this day, I consider Beeminder valuable and I recommend it to people - just with a bit of hard-won caution: double-check your mental state before you engage such a strong commitment device. Derailing needs to hurt, but if you're on a verge of spinning down into a dark place, it may tip you over.
Also: I love the "yellow brick road" chart, it's clean and junk free. A commendable example of good dataviz.