My favorite quote from all of the talks was something Reid Hoffman said. I don't remember the exact quote, but he said something like "A startup is a set of hypotheses that must be true in order for it to meet success."
I thought there was a lot of insight in that line. A big part of what we entrepreneurs do is make predictions about the market and, more broadly, about people in general. If our analysis is correct, and our prediction on the best way to exploit that analysis is correct, we have a very high probability of success. If we're living in a fantasy world (for various values of fantasy) then our analysis is flawed and it's much harder for our predictions to be correct. In order to be successful, an entrepreneur must see the world as it is. (Yet, as Brian Chesky illustrated, they must also possess tenacious endurance.)
Dalton Caldwell gave me a peek into a market that I've only heard vague stories about, which I thought was very interesting. As I've never sought funding, Paul Graham's talk did the same for a very different marketplace. I really liked those.
However, the most practical talk for me, personally, was probably Andrew Mason's talk or Adam D'Angelo's talk (despite its lackluster delivery). Those had the most takeaway for me.
I also caught a great one-liner from Reid (something to the effect of): "The big danger is not Google or Microsoft building your exact product -- they probably won't. The big danger is 1000 other startups building slightly similar, and you getting lost in the noise." (Except he said it better than I am restating it.) For me, that took a lot of things that I had understood but never really examined and crystallized them into an 'aha!' moment.
I liked Paul's entire talk quite a lot -- his thoughts on funding were typically well-stated and articulate, and it didn't hurt that they painted a hopeful picture for us as entrepreneurs. Hopefully the ripples of the changing investment structures in the Valley will spread to affect the general economy in a few years.
Find the flv file, copy the URL and download using wget or curl or whatever.