I used to prewash. Now I don't, for the most part. If I suspect a fabric might bleed, I test it. There are a few exceptions. Flannel can shrink so much, I do prewash flannel. I also prewash any fabric I intend to use for a bias binding, as shrinkage in a bias binding can ruin the edge. Because of bearisgray's observations about Michael Miller black, I also will prewash that specific fabric.
In my experience, fabric shrinkage is not an issue for quilts. This is because, once quilted to batting, the batting will prevent fabric from shrinking more than the batting shrinks (assuming a reasonable amount of quilting, such as 4" apart; if quilting is 10" apart, fabric can shrink more than the batting). If I want a smooth modern type quilt finish, without the "wrinkly" effect that comes from shrinkage, I use a polyester batting.
I have only rarely encountered a heavy bleeder fabric in twenty years of quilting. I more frequently find a few fabrics that will release a little dye in the first wash. This is because the manufacturer skimped on the rinsing, so there is excess dye (more dye than the fabric has been able to absorb) left in the fabric. To ensure these small bleeds do not color my finished quilt, I always wash the quilt for the first time with Synthrapol in a washing machine that uses a *lot* of water (in my case, a large front-loader at the laundromat). Water dilutes a dye bleed, and Synthrapol keeps the loose dye particles suspended in the water so they do not have a chance to settle in and color other fabrics.
This works for me.