Why I do support "Black Day" ... Yahoo has made it clear they want to make it a Facebook competitor at all costs. Instead of making a thoughtful, photo-centric redesign, which I'd welcome with open arms, they are glomming on social media skin while leaving the infrastructure intact.
The most recent redesign didn't fix things that were broken, and broke things that were working just fine.
Perhaps, when they debut a Facebook-ized Flickr, I'll end up liking it more than I did the last re-design. But participating in a "Black Day" posting is a way for me to give them notice that I'm not a happy camper.