How many times have you gone to lunch or drinks with somebody, tried to figure out who paid last time, and promised “ok the next one’s on me”? Happens to me all the time. I wish someone would build this app – “thenextone.com” – I go to lunch, hit a mobile site or send a text message, record who I went to lunch with, and who paid. Then, next time, voila! You know who’s turn it is. Presumably could even be integrated into foursquare or gowalla so that as you are checking in, it’s recorded. Done.
Bonus points for cross-referencing to my social network so the “I owe” is tagged onto the social identities for the people I owe or am owed by. Karma points for buying more than you are bought for…..