In one class, the instructor suggested that quilts be washed in Downy or a soap that is very gentle like maybe one of the detergents for baby clothes or a special soap for fine linens, even. Use cold water, don't agitate, just soak then drain the water...if using your machine, use the delicate cycle but don't wash for very long at all. She said that the detergent left in the fabric is what causes a quilt to collect soil. She dried her quilts for a very short time then spread them out to dry on a table or bed, etc. Lots of people like the vintage, old fashioned cotton quilts with the puckered look. By washing them this way, you don't get much shrinkage or puckering. Leaving them in the dryer longer will shrink them more if that's what you want.
Some people believe that quilt is a work of art and should not be used or washed. In my house it would really collect a lot of dust and be yucky dirty if not washed.