Meh, it means that the guy sending the email is a bit loony. It doesn't excuse responding in kind. Karp and Tumblr are a big deal. They should set a higher standard for themselves.
Its about implementing strategy for that.
"And this right here folks is why a startup is so extraordinarily stressful, why PR agencies exist, and why a squeaky wheel gets the grease." - Ramanujan http://news.ycombinator.com/item?id=2151989