I'm just learning to FMQ, and recently tried using fleece as a batting/backing. Previously I had only used W&N, so the fleece was waaay to floppy for me to control in comparison, and I did not enjoy the process at all.
That being said, I did really like the drape once it was finished...It had the feel of a quilt that has been well loved and softened with age. And, of course, fleece feels so nice to the touch.
Overall, I think once I have more experience with FMQ, I will probably use fleece again.