I used one (Fusiboo I think) for a smaller quilt and it worked fine, but by the time I was done ironing it on both sides to get it to fuse to both top and backing I figured it didn't save any time over using pins. The only advantage I could see was that I didn't have to take pins out as I quilted. I'm going to try spray basting my next quilt using Patsy Thompson's method of hanging the backing on a wall, spraying, applying batting and then spraying the top and applying that. I've always used pins, but I'm thinking that my aging back would appreciate using a method that didn't require lots of bending and reaching.
Rob