I absolutely prewash - warm water and soap - every single piece of fabric that comes into the house. 100% of the time, and I feel very strongly about it.
I have been washing my fabric (usually from my LQS) in the hottest water and with detergent - and sometimes fabric softener - and dry it in the dryer. Whoever gets the finished product may not know how to handle the quilt, and I may not be around to tell them.
So far, I haven't had any bleeding or running in my fabrics.