After my experience this week with not prewashing fabric, I'll never forget again. I bought a good LQS piece of fabric fussy cut a piece and realized that I'd forgotten to prewash (as were the rules for a swap). So I decided to handwash the piece, block it, and go on. NOT. The darn thing shrank a little more than 1/8 inch on all sides. Prewashing does make a difference. Back to the cutting board after I washed all the fabrics I just bought.
I think I'm going to take a page from a couple ladies on the board. I'm going go start pinking the edges before washing. That way, I'll KNOW what has been prewashed and hasn't.