I covered my crappy iPhone case in purple duct tape the other day.
It looked pretty cool, but it wasn't very practical. It didn't fit as well because of the duct tape folded into the inside. And all the parts I had to cut out looked messy. So, I just took it off. Shame to waste my pretty duct tape. I'm planning on buying a new iPhone case anyway, because this one is filthy and cracked. This is the one I'm looking at.