I expect PG and company are experts with regards to the needs of web startups and inexpert with regards to many fields of human endeavor. If you're going to be targeting one of those fields, mention the importance in ways which are easy for non-experts to understand. Our field is important: it employs X million, supports N companies on the Fortune 500, and did $ZZ billion in sales last year. Our problem keeps these people up at night -- they write journal articles about it, they spend hundreds of millions addressing it, it might even have killed a few thousand people they care about last year.
After you do that, people will be more inclined to view your solution in a positive light. Without the perspective of the problem, folks tend to latch onto things they understand about the solution: hmm, that button placement is off, this visualization lacks a bit of panache, I can't see myself ever really using this...
These are not the thoughts that typically precede writing big checks.
Interviews are only 10 minutes. We need random access; there is no time for sequential.
If you can do that I think you've sold yourself reasonably well as long as market size is reasonably resolved as an issue.
I would say showing that you're passionate about your company is important but it's not something you can make up. Having an actual product with real customers can easily help you prove your case.
I don't know if we would've got in without Garry from Posterous' help, so Tim and I are happy to grab coffee just like Garry did with us right before your interview and hear the pitch. Just let us know: email@example.com (goes to Tim and I)
While we're sharing, we interviewed and didn't get selected for S09 also. Leaving aside any flaws with the idea itself, I believe the main thing we should have done during the interview -- and didn't -- was coherently express how we were going to make a ton of money out of the idea. pg et al may totally disagree on that, of course, and there are other things that -- in retrospect -- could have a) been better or b) been communicated better. But that's my main 'I wish I'd said...' from our experience, anyway.
The other thing is demo. Ours really wasn't great - it was a screenshot walkthrough which didn't show the tech in action. We had to do a lot of talking to overcome that, which meant not enough time to talk about everything else. If your demo explains everything in 30 seconds, you'll have a way stronger foundation than we did.
"Another way of approaching this challenge is to think: what's different about what you're doing? If the only thing that's different about what you're doing is that the product is easier to use, then you need to think long and hard about a better way to differentiate yourself."
I would also stress the value propositions and benefits of your solution and how those are exemplified in the features. It'll make for an excellent transition into the demo and not read like a boring feature list.