Man, I feel your pain. I have developed the most awesome products the world has never seen 4 times now. We had a "build it and they will come" attitude too :( We decided to ask ourselves one question: How to we validate an idea before wasting months on an idea that only we seem to think is cool? So we are creating WillThisFly? to ask that very question... it's a site that allows you to try out your ideas and projects…
Sometime it just need a few more optimization iterations. Considering the Facebook example and prior art, this must be really frustrating for those who missed the gold pot.