Yes. Number 1, product advice, and number 2, advice about dealing with investors.

http://ycombinator.com/about.html

http://www.paulgraham.com/ycombinator.html

I think the value of contacts and credibility should not be underestimated. On both ends, really. You have to trust your investors as much as they have to trust you, especially if you don't retain 51%.

YC has a lot more credibility than most other entities when it comes to choosing the right startup or the right investor. I would be significantly more likely to accept an investor who was introduced to me by pg.

Would it be possible to publish your product/dealing with investors wisdom into a book?

The essays I've been writing about startups are going to be such a book. Most of the general advice I could give about investors, particularly, I've already given, in e.g.

http://paulgraham.com/fundraising.html

http://paulgraham.com/investors.html

http://paulgraham.com/startupfunding.html

Your Submarine essay on PR has been especially valuable advice. I hope it makes any folio/book.

It helped my tech-startup to gain the courage to spend a realistic amount on such a vital area.