Google Search Weirdness: Hmm... the results for your search don't seem very relevant

I have seen numerous reports of Google showing very weird search results, or lack there of, followed by a message that reads "Hmm... the results for your search don't seem very relevant." It just seems like some weird bug, a possible plugin that is impacting the Google search results or something else. But it is too wide spread to be a weird plugin, so maybe it is some weird Google bug or feature?