On most countries, traveling abroad for a convention or a professional event is considered a tax reductable expanse for those of us that are self-employed. This is actually, where the beta site of Eventful becomes really handy.
Planning a vacation in New-York? Search for a lecture or a convention nearby, and deduct all of your expanses. Eventful holds a comprehensive list of events all over the world, indexed nicely in a web 2.0 technology.
Eventful also lets you publicize your own events or demand an event from a registered performer.