Make sure that the jeans you actually pick for the quilt aren't *too* worn, or you'll regret it down the line. I have two denim quilts, and my faaaaaavorite one, the one named "the nap quilt," over which there have been arguments over whose turn it is to use it? It's falling apart, because the denim patches that all came from one particular pair of jeans are all wearing out. I refuse to get rid of the quilt, but the patching is getting tedious.

Also, just a warning- sewing through layers of denim is difficult, and sewing machines don't like it much. Take it slow, have extra needles around, and consider getting the needles they make just for denim. You might still break a needle (or three) but your chances are better.