I am in the process of making some small quilts from shirts for some friends. I have found that for the most part they work just fine. It is a good idea to sort the fabrics by weight; in that you will find some lighter than others. For the lighter ones I found it necessary to do foundation piecing. Use lots of starch. Lots of starch. Lots of starch.
A good read would be Bonnie Hunters website: http://quiltville.com/
There are a lot of places there to click and see. She has written a few books on the subject:
Scraps & Shirttails
Scraps & Shirttails II

If you like scrappy quilts, this is one way to bust that stash.