I tend to agree with 1st of 5 and The Big A. I get the so-called "Pandora fatigue" pretty easily. About the only times I listen to Pandora are when I have a craving for a particular artist, though I'm beginning to find Slacker does a better job at that than Pandora, or when I'm traveling, and that's mostly because Pandora's app is the only one that recovers seamlessly from network drops.
When it comes to Pandora being a threat to radio, I don't see it as being much of one by itself. When it comes to the "Pandora fatigue," I didn't coin that term, and I'm not the only one who suffers from it. While Pandora leads in session starts, the average session length is about 90 minutes. The only pure-play webcaster that has an average session length of greater than three hours is AccuRadio, and several terrestrial broadcasters (including CBS Radio and K-Love) have average session lengths of more than three hours. I seem to remember Clear Channel's session lengths average just a hair less than three hours on average. In other words, Pandora's session lengths are pretty anemic when compared to terrestrial.