Hmmm I was rejected this past April and then sent a reply back saying something like your loss.

Miraculously a week later I was invited out to Silicon Valley to demo our novel tech, though not to Y Combinator but one the biggest tech firms out there. Not sure how that happened ... people talk, I guess.

So if you don't get in to Y or others I say send a reply making them doubt their decision. This worked for me this past April and more so in 2008 when I was accepted into another popular incubator program.