1) Introductions to prominent VC's/Angels if you want to obtain further funding
2) As a result of the process of getting into YC, it can somewhat validate your idea
3) Having to pull it off in 3 months can really light fires under people's asses
4) PG seems like a genuine bloke who really wants to help people. The mentoring aspect would be worthwhile.
5) Constant feedback. You'd be surrounded by a lot of other YC alums who are very switched on people... Good things to be learned all round
I'm sure there are other reasons I failed to mention, but I think I covered the basics.
EDIT - also, read PG's essay on the subject.
I'll assume for a moment that you are presently a "good software developer contractor" and you currently gross "$10k" a month.
Given that, $10k a month is your opportunity cost for doing something else, for instance, doing a startup.
That fact has little to do with your question "is ycombinator worth 5% of my biz for ~$15k"?
If you want to do a startup, then you'll be giving up your $10k a month to build something that scales beyond your time. I recommend doing this, if you have the risk-tolerance for doing a startup.
IFF you decide to do a startup, THEN you have to decide how to fund it. YCombinator offers your team ~$20k for 5% of the company to kick off your startup efforts. Plus, they offer you the "prestige and access" you'll get due to YCombinator. The alternative is bootstrapping, or "normal" funding channels.
From what I know about YCombinator, it's definitely an outstanding opportunity if you can get your idea accepted. If you're young and inexperienced and mobile, do it.
Alan
We are self-financed and so we do contract to pay our living expenses. It is working great for us, but often we will get sucked in client projects. Those distractions have been costing a lot in term of growth. 5% for the intros and money to just focus on your idea for 12 weeks is certainly worth it.
Also, the adage "it's better to have half of something than all of nothing" has never let me down. I've always been very generous with stock and it has always paid off -- for me anyway.
But Demo Day is worth a lot more than 5%.
... just saying. I'm applying next round and for me, the money is low on the list of what I like about the YC prospect. It's a nice thing to have don't get me wrong, but it's really one of the smaller pieces of the pie in my opinion.
The right question is something like "Is ycombinator worth the equity it will cost my company?"
While other people have talked about what ycombinator is worth, the right answer to that question also depends on the meaning of "my company".
I think that an elite college degree is worth $150k for most people, but I don't think it's the connections that add the value, so much as the prestige of the degree, the recruiting opportunities, and the information learned (mostly outside the classroom) about how the economy and society actually work.
The recruiting opportunities are part of the connections too. The information that you learned outside of class is mostly from your connection outside the class too.
This may not be a strong case for a local resident in US. For my case, I did have a stronger connections(friendship) than in my country(Malaysia). I am sure that I cannat achieve what I have done so far here if I decided not to further my college in US.