We, no joke, ultimately were able to drop our support for IE6->8 because of the youtube "we are dropping support for IE" banner. We spun it to our bosses as "If google is doing this, we should be able to."
Which, if you haven't read it before, the story of how they did that is worth the read.
Some time ago there was a post here about it. The guy claimed he and a few other fed up devs made that banner on their own initiative. The whole thing was a huge bluff because at the time google had no such plan but it gained so much momentum that they went ahead with it eventually.