Well I finally took the plunge and did some felting. I used Crystal's flat bottom bag method (http://crystalkini.blogspot.com/) to make 3 different felted bags with 3 different brands/types of yarn. I did one with Patons classic wool (red), and one with Jo-Ann's Sensations Bellezza Collection Dolcetto which is a wool/cotton blend (purple/pink), and the final one with Jo-Ann's Sensations Bellezza Collection Tesoro which is 100% wool (purple).
The Patons did great, as did the Dolcetto (blend), but unbelievably the Tesora (wool) stretched all out of shape and grew at least twice as big. I would have thought the wool/cotton blend wouldn't have felted well, but it felted beautifully. I've also got a small bag going, and I'll get pictures of it up soon. :)