I did this once:
BERLIN (Reuters) - A 21-year-old German tourist who wanted to visit his girlfriend in the Australian metropolis Sydney landed 13,000 kilometres away near Sidney, Montana, after mistyping his destination on a flight booking Web site.
...only I was fortunate enough to catch it within 5 minutes of clicking the purchase button. I was booking flights from Kansas City to Orlando, to pick up Reagan from her semester working at Disney and was going to take her directly to NYC to visit my Aunt. Only, I had purchased tickets that start in NYC then go to Kansas City and then end in Orlando.
When I found out that I had bought those tickets, I freaked out. I spent almost $900 on tickets that I wasn't able to use! It was turning out to be a very sad day, but the people at Expedia are awesome and fixed it for me.