I thought it was funny...
While at Michaels yesterday (looking for stuff for my daughter's b-day party), I saw t-shirt yarn for sale in the center aisle! I don't think it was called the same and probably wasn't made out of recycled t-shirts, but it was the same idea. I was just surprised because I hadn't thought it had become so mainstream!
Here is the TUTORIAL I used to get started making t-yarn
(P.S. it's much less expensive to make it yourself~ especially if you use t-shirts you already have).