To be honest, I’ve never had a plain cup of coffee at Starbucks, but Marketonomy has and the author thinks that the horrible taste of the plain coffee is designed to push the buyer into buying a more expensive coffee beverage:
When a Starbucks opened right next to my office, I found myself buying more of their crappy coffee, and then upgrading more frequently to a Latte just to avoid the torture. When I finally graduated completely from coffee to the poodle drinks, it struck me: Crappy coffee is an upselling opportunity. It's what everyone initially comes for, it's the cheapest thing on the menu, and it sucks. But for just a few dollars more, you get flavor. Any flavor you want. Any combination. And once you make the initial leap, a banquet of delights appears before you. Add a little chocolate, a little orange, a little cinnamon and whipped cream. It's just money. And once you buy a Starbucks' loyalty card, you won't even tally up the transactions any more. Just dump some cash on the card every payday and you're good to go.
Read the rest of the post because it’s an interesting take on Starbucks.