It looks like Catrina Fake has already left, and Stewart Butterfield is on his way out on july. Stewart is apparently known for his wit, and he has submitted, in my opinion, the funniest resignation letter, I have ever seen. To give a brief background, Flickr, a photo sharing website, was founded in 2004 and was acquired by Yahoo in 2005.
Here is the letter for your reading pleasure.
(Source: valleywag)