Starbucks and Twitter have partnered for a “tweet-a-coffee” program, enabling $5 electronic gift certificates to be exchanged via tweets. Previously, Twitter teamed up with American Express for purchases made by hashtags (#_.

Twitter’s expansion of their advertising opportunities through such executions could indicate that advertisers are gradually beginning to see value in Twitter as a potential e-commerce platform. Only time will tell how successful these Twitter programs will be, however, given the disappointing performance of a comparable example: Facebook Stores.

On the other hand, this could simply herald a forthcoming couponing ad opportunity, following in the footsteps of the more effective Facebook Offers and Google Adwords Offer Extensions.

In the face of a looming IPO, it will be interesting to see how Twitter further expands and distinguishes their (and Vine’s) ad offerings.