Forbes has a monthly Red/Blue series where they "investigate how consumer political affiliation relates to brand perception." Here's what they found about Starbucks:

Democrats and Republicans started the year with a marginally different perception of the brand: a Buzz score of 15.7 for blue and 14.6 for red. Fast forward to this week, and perception is at 19.3 for blue and 10.7 for red – both scores are positive, but there is a definite partisan divide. The perception is measured by YouGov BrandIndex’s Buzz score, which asks respondents: “Have you heard anything positive or negative about this brand?”

... we see partisanship at work in the coffee chain’s perception. Earlier in 2012, the brand led some right-wing consumers to go elsewhere for their daily cup of Joe after it supported a gay marriage bill. Joining fellow Northwest-based firms Microsoft and Nike, the company said in January that it was: “Proud to join other leading Northwest employers in support of Washington state legislation recognizing marriage equality for same-sex couples.” The conservative group National Organization for Marriage launched a “Dump Starbucks” campaign in response to the coffeehouse’s decision. Perception after the statement consistently increased for Democrat consumers and decreased among Republicans.