There's a new partnership in town. Twitter and Starbucks joined their forces to enable users to gift each other Starbucks coffee via tweets. Bestowing a $5 latte on someone has never been easier. One just needs to include @tweetacoffee and the recipient's Twitter handle in their tweet, and the above mentioned latte is on its way either through adding the gift amount to the Starbucks card or printing the eGift.
Twitter has already proven in its partnership with Amex that it can be a quite robust digital commerce platform. Starbucks partnership takes this premise further. It is not hard to imagine how Twitter can evolve from current deals & discounts to gifting and to actual monetary exchanges. The critical advantage that Twitter has as a platform is a load of existing social relationships and content, both of which are highly coveted context for online transactions.
The mechanism seems simple enough, and it will only get simpler. Neither technology nor user behaviors are a barrier here; it's the retailers that are slow-moving.