A tweet can be used to share links, media, and status updates. But could it soon be used to share Starbucks coffee? That’s the promise of a new partnership between Twitter and Starbucks which enables gift certificates to be exchanged via tweets. Called the tweet-a-coffee program, the service allows for spur-of-the-moment acts of generosity between friends, with little to no friction: Just tweet at another Twitter user in order to give a $5 digital eGift hassle-free. It’s certainly a novel marketing tool. But the larger significance here is how companies like Starbucks are gradually beginning to see Twitter as a potential ecommerce platform.