Where I’ve Been, a Facebook application that shows your friends which countries you’ve visited (and the ones you’re planning to visit), is reportedly sold to Tripadvisor (a travel review site) for 3 million dollar.
Where I’ve been is one of the most used Facebook applications, with 2.3 users. This would give the sale a 1,30 dollar/user valuation - making it by far the biggest deal for a Facebook application this far.