I am in the process of making a quilt from all my running t-shirts-I probably have enough to make two or three king size ones. But it's a long process and I only cut the squares after I have worn the shirt for a while or just hate them (someone needs to have a class on making cool t-shirt logos, as I usually end up with a bunch of the uglies).
On Thanksgiving, I did a Turkey Trot 5K in Lansing and in the gathering after the race, where all the frozen, damp runners hung out was a woman who has written a book about turning t-shirts into quilts with several of her creations. You can visit her website here and be sure to check out the story of Chad .I am sewing my quilt squares by hand where she is doing the actual quilting by machine (I prefer hand sewing in general which is how I learned to hem, quilt and embellish etc). The book is available from both her website and Amazon if you are so inclined. Everyone has t-shirts-I was just weeding out my stash again this week, to make room for more. I also have running sweatshirts that would make a very warm cozy.