You make two paper bags and put a rose in each… [Y]ou mark one of the bags “Rose” and the other bag, although it also has roses inside, you label “Mowed Grass”… Then you invite people to sniff each bag… They they have to rate how pleasant the smell is, how sweet the smell is… And it turns out that a rose by another name—Mowed Grass—does not smell as sweet. People overwhelmingly said that the bag marked rose smelled to them, sweeter.
NPR has a fantastic interview with Lera Boroditsky, in which she describes this and a few other experiments she and her students have performed. She's also written How Does Language Shape the Way We Think?, which goes into more detail (though not about the rose experiment).
(via Lost in Translation)