BufferOverflow.com is currently unregistered, and can be reserved. Possibly for "defensive registration", as Spudley suggests in the comment below. Until there's a use for it, it can be a redirect to StackOverflow.com.
Why again do you think bufferoverflow is special??
99.9% of stackoverflow/stackexchange traffic doesn't come from manually typing the URL. And of the 0.1%, 99% of the people who will type it actually know the correct name, and no sane person will go to bufferoverflow.com for no reason expecting to find help on the other end.