How can a person use accountabilibuddies to be more productive?

Lately, you've mentioned using accountabilibuddies to help break bad habits, cultivate new habits, get more done, or eliminate procrastination. How does that work? What kind of person do you want as you accountabilibuddy? What do you do for them? What do they do for you? What are the major benefits? What are some of the pitfalls to avoid?