I've made several flannel rag quilts and what everyone else is saying is true. I would also like to add that I think it depends on your washer as well. I made one for my grand daughter and washed it twice in my front loader. It looked ok to me. Then my daughter washed it again with baby soap in her top loader and she got handfuls more of the lint and little strings. I think some front loaders are just too gentle.
I read somewhere that the guy that sells those hand held quilting frames suggested taking them out on the driveway and taking the weed whacker to them. There were pictures on his website. I would have a mess if I did that.