I saw a battery operated product for trimming wallpaper at some
trade fair a while ago. it was called eazytrim or easytrimmer

the tool was pressed into an angle or corner onto the wallpaper
and it had a sewing machine type action which perforated the
paper and left a very neat, clean edge.

amazon have the details but it's discontinued http://snipurl.com/q7xz

anyone know where I can buy one online or in the shops ?

got a /lot/ of wallpapering coming up and would like to make it as
easy and as neat as possible. I've got a rotary wallpaper cutter
but I find it to be hit and miss at best.