This actually strikes a chord with me because I started hanging onto all my "fat" jeans as I lose weight...this would be a perfect project for all of them!!
I agree with those that posted about using larger sections. I am currently working on a quilt for my husband using his Army uniforms, which is a pretty heavy fabric...I made on Ohio Star block and wow...what a pain! The fabric is just so thick that the seams were very bulky. I still did it though!
But, for your sanity...I would try to cut them into AT LEAST 5" squares and have at it! Good luck!!!!