There was a 500 startups group (I believe from their last demo day) called PayByGroup that is also doing group payments such as this. It seemed to me that the

There was a 500 startups group (I believe from their last demo day) called PayByGroup that is also doing group payments such as this. It seemed to me that the most promising application of such a feature is as a button on existing sites, not as a stand alone site/app. The example PayByGroup mentioned in their pitch was having a 'Pay By Group' type button on AirBnB for crowdfunding a trip. That seems to be the easier route to mass adoption than trying to create a new destination in my opinion.