I've seen lots of projects made using t-shirt yarn and I've been wanting to give it a try. You need to start with a t-shirt that doesn't have seems in the side and then you cut it so that it ends up in one long strip and you can crochet with it.
I got one of Wade's t-shirts (with his permission) No seriously I asked him and he even picked one out that I could cut up.
I didn't really make anything with it but I did crochet a circle. I used a large hook and the ball of yarn didn't go as far as I thought it would.
I do believe I would like to do more of this though. I'm thinking that a thrift shop with super cheap XL t-shirts might be the way to go.