Scraped off old wall paper today. Luckily the glue was water soluble, so a spray bottle with water, this nifty tool to perforate the wallpaper and a scraper did the job. See here how to use the perforator.
The spiky wheels make holes in the wallpaper so the water can go through and dissolve the glue.
Shortly after we moved in, I painted over the wallpaper with sunny yellow as a quick fix. I was surprised today, to find almost the same yellow under the wallpaper!