The case of where you have something really great that you want to search because it could mean a huge impact on something, or do something big, e.g. change the world, make a new internet meme, etc. but as soon as you try to, you instantly blank-out, and forget. This is really annoying.
I had such a bad case of Internet Forgotten that between the home page and the search page, I forgot what I was going to search for.