@oulfis raised another good example, along with a post describing additional Beeminder goals added to try to solve the problem:
I would say Beeminder avoids the Goodhart-type problem where a manager or politician sets a bad metric and the people assessed by it can’t change it, since with Beeminder you are the one setting your own goals.
But any goal-oriented approach is going to be subject to the Goodhart-type problem where you set a goal that seems to make sense, but you end up unconsciously gaming it to some degree - which is why it’s so helpful to set up a regular review to see if your goals are actually working for you.