I'm not sure actually, thats a good question and I sent a quick email to their support to find out. I didn't know that Pandora was running at 64 kbps mono and it sounded great to me in the car so I guess my quality standards are a lot lower than you guys!

From the Simplify Media FAQ:

How does Simplify Media work?

Music is streamed directly between computers over the Internet within small groups that you control.

So does that mean I'm serving the song up directly from my computer when I'm listening to it? If so maybe its streaming at the full bit rate? That might explain why some of my songs take longer to load than others.

I dunno just a guess.