I used it some years ago. You have to figure out how to use it and for what things it will work for you. As an example, for me having any daily task tracked with Beeminder was a huge hassle. I don't want to have to open an app and update several items I'm tracking every day. Others are fine with this. For me, goals with a longer cadence ("once a week") work better on Beeminder.
Also, initially you'll not know what you really want to track in Beeminder and what you don't. I did find myself cheating on occasion. If that happens to you, consider whether you should even be tracking this at all via Beeminder.
Beeminder can give you a bit of hyperfocus. That task that will cause you to lose money today if you don't do it? Becomes top priority for you that day. I found the items I was Beeminding were getting done, but perhaps other more important items I was not putting into Beeminder weren't. In a sense, after a few months of use, you could say that Beeminder will give you an idea on the importance (or lack of) of the things you are Beeminding.
For these reasons, I did stop using it. I'll probably return to it one day when I figure out my priorities. I heartily recommend it to others, though.