Another thing that came up in the Slate Star Codex discussion:
More fundamental to Beeminder than magnifying negative consequences is, exactly as Gudamor says, bringing the negative consequences SOONER. You have to have your datapoints on Beeminder’s yellow brick road every day, making slow but steady measurable progress.
That’s in fact Beeminder’s key difference from all the other commitment device apps we know of, which we list here, btw: http://blog.beeminder.com/competitors