At one of my worst days at work, my eccentric 40-ish, sci-fi conference-attending, lesbian teddy bear collecting colleague sent me a link to the site.
London bombing
In London during the 7/7 bombings, I was outside the London ambulance service handing out tea to the EMTs. One of the comments on metafilter was that tea made everything all right to the Brits :)
But the thing that made me sign up as a member was absolutely the portobello mushroom thread.