A few years ago (October 1998) here in the US that was aired on television. A man named Lenny Montano (or Leonardo Montana) who went by the stage name of "Valentino", and was later called "The Masked Magician" did that.
He did a series of 4 shows where he was were a mask so you didnt know his identity, and reveled how a bounch of big tricks were done. On the last show he revealed himself and gave a big speech on how he was tired of magicans doing the same old tricks, and how this would force alot of them to make up new material. Well although there was some truth in his speech, it was still a horrible thing to do.
If you want some more information on this moron and why he did it, heres the link:
http://magic.about.com/library/weekly/aa103098.htm
Here is another link I found about magicians exposing secrets in general, including the valintino story and also about Richard Robinson:
http://www.billpalmer.com/exposure.htm