Bonobos is currently running a viral giveaway on Facebook: Win a Wardrobe. Giveaways on Facebook aren't unique - they are great ways to drive Facebook fans, sharing and awareness. But what is unique is the viral hook that Bonobos is using:

"The more you share, the more chances you have to win."

That too isn't unique - usually contests give extra weight for the number of shares, referrals, etc. Bonobos is doing it differently though - and its very clever:

If one of your friends wins, you win the same prize. That's different and very cool. If the prize is enticing enough, its a more interesting way to incent referrals and sharing.