Oath is a web based app that works to create a community of users that challenges its users to be different. Oath users will create an Oath and invite a 'Oathee' to meet the challenge.
Have a friend thats been a little flaky? Invite him or her to your next event, or function and give them THE FACTS [TEXT MESSAGES IN 10 MINUTE SUCCESSIONS FOR A DAY] when he or she doesn't complete it, or to up the ante, attach a monetary value to the outcome.
This hack is one of the most entertaining ways to keep you and your friends honest.