This is a great collection and observation of illusions. Optical effects have the great ability to really get observers to interact with what they're presented. I would agree though that successful and desired effects were stated in, "Devices and Illusions only really work when their use is entirely justified and supports the central premise of a campaign."
There are a lot of great examples used in this article. I've even looked at "See Saw" (the UMD library has this) and saw lots of additional techniques that could be employed. These are things to keep in mind when you want to quickly gain a viewers interest.