I have been talking at events for years, but in 2005 it was the first time I was invited to speak at one of the major search/advertising events. 2005 ad:tech had the claim to fame as being the the first major US conferences to be held in Asia.
While ad:tech isn’t a search specific event, it is probably the largest advertising conference circuit. My speech at ad:tech would be focused on letting people know what SEO is.