karebear - I've found 3M Command Adhesive hooks hold really well on the smooth bathroom surfaces. They come in various sizes and can really take the weight. On wallpaper they hold really well to the wallpaper but the wallpaper doesn't always hold so well to the wall. They also sell only the adhesive strips which I've used to help hold on a stick to the wall TP holder much better than the adhesive supplied with it. They are also easy to pull off if you change your mind, which is surprising since they hold on so well.
—Gary