Speaking of wall decals, it was around two years ago that I first discovered them via What Is Blik. They consider themselves the world's first removable graphic company, providing "wall graphics for the commitment phobic". Back then I spent hours and hours pouring over the website, trying to decide which decal could work for our living room and bedroom. I never did choose one!
I've heard that they can be quite tricky to install, and I'm not sure they're quite right for our 1927 Spanish Style apartment, but a few of my favorites below:
I also just discovered Surface View, who have an incredible range of images that can be applied to walls, canvas, even blinds.
The beetle is kind of amazing, if a little creepy!
I think the only danger is overdoing it i.e. using one in every room!