Seems some scientists had a bit of extra grant money lying around and decided to check whether or not people could really tell the difference between Pepsi and Coke.
The result? "When asked to taste blind, they showed no preference. However, when the participants were shown company logos before they drank, the Coke label, the more famous of the two, had a dramatic impact: three-quarters of the tasters declared they preferred Coke." This indicated to researchers (along with the brain activity being monitored) that the associations that people had with the Coke label and logo were such that they actually influenced the way people experienced the drink.
I've always thought that I could tell the difference between the two. I've always thought that Pepsi was a bit sweeter and a bit smoother. Coke seemed to have a bit more edge to it. Now, well, I'm just going to have to test for myself maybe. If I do, I'll let you know what happens.