I realize it's not YC application season (edit: actually it looks like applications are open), but I figured I would post now since I would undoubtedly forget later.
A friend and I applied for YC Summer '09 for a search related company (actually what Greplin is doing now). We made it to interviews but didn't make the final cut.
I went on to do other things and about a year later ended up back in start-up land with a different co-founder and a different idea. We just closed a multi-million dollar deal on fantastic terms yesterday from one of the best VCs in the valley.
So the moral of the story is this: rejection doesn't matter. To quote Randy Pausch: "The brick walls are not there to keep us out, they are there to give us a chance to show us how badly we want something." Raising funding is only the beginning of this journey but if you didn't make it into YC or face a similar situation somewhere else, exceptions to the rule do exist (like us) and there's really no reason YOU could not be another.
Cheers!
(if you know who I am, please keep my identity a secret, thanks!)