Last week I made a t-shirt quilt for a customer using her husband's shirts. It turned out quite nicely, if a bit plain. The black that she chose really makes the colors in the shirt graphics pop.
At first I didn't like making t-shirt quilts, but as I have had more practice, they have really grown on me. I doubt I will be making them for my children because they tend to wear their shirts out.
If you make one of these quilts, remember that the interfacing for the t-shirts is key. It has to be the stretchy kind. And when quilting, raise your foot a little to make sure you clear the fabric and seams.