I have a lap quilt that I used this flannel on the back. It's been well-used and washed monthly for about a year now, so pretty good usage. The back isn't exactly pilling but it's starting to get these lines of fuzz on it. Sort of like pilling, but long rows of fuzz rather than little balls of it. At some point I'll probably take one of those sweater shavers to it. It started happening about 6 months ago.
I think their flannel is OK for rag quilts, but I don't use it for backing anymore, because of this. It's not terrible, but I don't like it. Connecting Threads is my new favorite place to buy flannel - it's so much thicker and more luscious right from the start, and it lasts longer too. A little more expensive, but I think it's worth it.