A common problem around the office is "who will I eat lunch with today, when, and where".
It's especially bad when you have several groups of friends working in different nearby offices and not the same office/company - you can't just shout down the hall "where do you guys want to eat today", but you need to coordinate with every one of them independently (I usually don't mix groups, but rather eat with friends from one group at a time).
Is there a webapp / Facebook app for organizing casual lunches? Somewhere I could post "I want to go to eat at Sushi place X or Burger joint Y today", who's with me?
One implementation is simply posting this to my Facebook status, but that's hardly efficient.