I use precuts a lot because I do like the variety of go-together fabrics and colors in them. I don't think I have ever got a perfectly cut package. I also have never got a perfectly squared panel. It really is the "nature of the game" with fabric, and until the fabric companies start using die cutting or laser cutting machines, that is just the way it is. To my knowledge none of the fabric companies are doing this - all the fabric is being hand cut. However, I have heard that Hoffman has bought a die cutting machine and will start using it soon for all their precuts. I heard that about a year ago from a fabric rep at my LQS, but I haven't seen any results yet. I am still waiting though. . . .
Also, I have read and been told that you should never prewash precuts.