All good advice. I'm rehabing a house now and having a heck of time removing the old wallpaper. After a couple gallons of DIF, the glue back was still stuck to the wall. So here's what I did.
I re-scored the walls, then applied extremely hot water with a heavy nap paint roller, completely saturating the paper. Let sit for not more than five minutes (you can tell when the glue softens) then carefully removed it with a wide blade putty knife.