Here's another unusual invitation stunt from DDB Stockholm for Stockholm contemporary art gallery Bonniers Konsthall (last year's project, The Uninvited, sent notes to recipient saying they weren't invited, but could invite a friend).
This time, to generate buzz around a new artwork, people were invited to an event via Facebook - but told that if more than 99 people agreed to come by 9pm, the event would be cancelled. The sign-up started at 9am, and the first 99 to respond got the incentive of a silkscreen-printed t-shirt (which they also forfeited if the event was cancelled). They could choose whether or not to invite three more people. The fine balance between wanting to come and wanting not to share highlighted the gallery's message that it is 'not for everyone', even though the 'event' was eventually cancelled when 101 people responded.