A couple of local (or internet-local) bands. One BBC documentary about a particular subculture that I was interested in at the time. One (fairly obscure, but involving some minor technical firsts) video game.
All pop-cultural ephemera perhaps, but the sort of thing that qualifies as knowledge in my book.
Also note that I didn't say destruction of knowledge, but destruction of value(data), which is a very different thing. I don't need to care about pokemons, or star trek episodes to understand that some people might be interested in documenting and organizing those. Maybe Wikipedia isn't the place. It doesn't mean the Wikimedia foundation could not provide an open solution.
edit: it's a serious question! Instead of down voting, just tell me. Or even downvote, but at least tell me.