I had an idea for a band called 'monkey vs. robot' in high school, but that ended up being taken.
I designed a way to mass-produce semiconductor chips using laser-splitters in middle school, but I think that was around then too.
Today I had an idea for a website, http://www.sploogle.com , but if you go there you'll see that they already did exactly what I was going to do with it.
Original ideas aren't so original anymore.