As for the friction of adding data, we have smartphone apps and an email and SMS bot to try to help with that. But ideally you automate it. There are dozens of apps and gadgets we integrate with (RescueTime, Fitbit, Trello, Garmin, GitHub, etc etc) and we have an API, or you can make an IFTTT or Zapier recipe/applet/zap/whatever.
Oh yeah, and I should point out https://blog.beeminder.com/cheating
Finally, good point about being careful what you beemind. We try to minimize the danger of that with our one-week "akrasia horizon". You're never on the hook for more a week into the future, i.e., you can stop or change a goal at any time, with a one-week delay. So you haven't lost much if you realize you're beeminding the wrong things.
Or if it's just that more important things are getting crowded out, our self-serving advice is to just beemind those things as well!
Thanks again for this comment!