That's hard. There are plenty of bands that I know I'm probably going to buy, but the Internet and iTunes makes it possible for me to always listen before buying. It's habit at this point. Also, so many of my favorites have eventually put out a bad album...Ani Difranco, Counting Crows. So from my jaded perspective, I would only buy unheard if I absolutely could not find sound clips online.
M. Ward
He is fantastic. More people should know about him.