I think it would make sense if you can show some improvement over the last application period or if you think you have a better idea. If you're just applying just for the sake of getting something in on the off-chance it might get accepted, then you start to look like that person who shows up at every American Idol tryout but hasn't done anything to improve their chances.

I wrote about us applying multiple times (and eventually being accepted) here:

http://blog.directededge.com/2009/09/30/on-applying-to-y-com...

I get the impression that there are quite a few YCers that didn't make it on the first application.

PG has said in the past that the most compelling argument you can make to investors is that you're going to keep forging ahead, with or without them. At the end of the day, YC are investors too.

It would seem like the best approach would be to apply with a better version of your original app, because that illustrates that you are persistent (you weren't just looking for an idea to get in with) and can improve upon the initial concept. Best case scenario, IMO, your idea is the same but with more traction (I'm assuming of course there is/was a prototype involved).

According to PG sometimes you dont get in, not because there is anything wrong with your application, but because there were so many others who were a better fit. In this case applying again isnt productive. And you shouldnt change your idea just to get into YC. Right?