After further experimentation, I found that the direction the spring is pulled away when the "keep" and "delay" qualities are used is always opposite the direction the spring pushes you. This means the sping can levitate after you touch it. It stops working, even if you can still touch it. The coolest this with this was one well placed TNT caused the spring to push me straight sideways, which made the spring slide sideways half a tile, and looked perfectly usable, although it didn't do anything when I touched it.