You may be pleased by a 50% success rate, but how many of the 50% who don't succeed will be pleased?
(Not just being facetious -- I've heard stories about YCers whose companies failed being hired by other YC companies or otherwise finding good positions as a result of their YC experience, but a few anecdotes is no substitute for data.)
I fall in the 50% who did not succeed. I stepped down from Contagion Health (imoveyou.com, S2010) at the end of our batch, but my co-founder Jen is still at it and looking for a new co-founder.
Reasons for failure aside, I have no regrets at all. It was a completely amazing experience with amazing people and amazing opportunities. I'm still very close with many companies from my batch and actively helping a couple of those.
I can't say I would have done anything differently since I wouldn't want to miss out on any part of what happened.
"Not succeeding" is not so bad. Life goes on while I work on my next project, this time focusing on building revenue instead of raising money—a refreshing change. I don't know if my current project is a great fit for YC yet, but I can definitely see myself applying for YC again someday.
Most of them. Those who don't succeed have a big pile of successful startups who know them well and will hire them (if they stil have the startup bug). They've gotten a guided tour of the valley-style startup path-- next time will be easier.
It'd be an interesting experiment to track down all of the YC companies that have fully failed to date and ask them, "knowing what you know now, do you wish you'd chosen a different path?" My guess is that 90%+ would do YC again in a heartbeat (though perhaps with a different co-founder or different market/idea).
I've heard stories about YCers whose companies failed being hired by other YC companies
I've heard successful YC companies referred to as being like piranhas (or something like that). Any time another YC company shows signs of failing, the others tend to wonder about hiring opportunities.
(Not just being facetious -- I've heard stories about YCers whose companies failed being hired by other YC companies or otherwise finding good positions as a result of their YC experience, but a few anecdotes is no substitute for data.)