I think social accountability would only work if (1) someone else could tell whether I'm cheating (that's not happening in a personal project) and (2) cares enough to check my graph.
Maybe my cheapness trumps my integrity. Or more positively, I reframe the meaning of the price: what does $5 buy me in Beeminder? an accurate data point. Is $5 worth an accurate data point? depends on what I'm planning on doing with the data later. And because I don't know what I want to do with the data, an accurate data point doesn't seem very valuable.
That's really unfair, though. I know that losing those $5 eventually will coax me into complying, but my inner Hyde will convince me to lie. Sigh.
I guess I just don't fall into the target niche (although it really looks like I do—except for the cheapness-trumping-integrity issue).
Or maybe a better answer is to automate the data entry (we have dozens of integrations -- GitHub, Trello, Fitbit, RescueTime, etc) so that you'd have to do more than lie to the app. With enough effort you could still cheat, of course.
Would love to hear if this is overcomeable or a dealbreaker!