It's an interesting post but I don't think the statistics actually support the conclusion. The 1st blog post referred 1'500 people -- we don't know how many actually visited the blog post. The second post had 3'000 visitors. Without knowing the bounce rate from the first post we can't compare these stats.

UPDATE: The other point to consider is that this is purely post-hoc reasoning. I can think of at least one alternative explanation -- the people who arrived from the first blog post were already motivated enough to click another link so they were more likely to purchase. Without doing some kind of experiment to differentiate these hypotheses we can't make a judgement one way or the other.

It probably sounds like I'm raining on the author's parade. That's not my intention. I really like that he's put these figures online and is trying to analyse. I hope I'm just showing that the issues are more subtle than they seem at first.

It's also a very good example on how to use HN to get exposure for your product:

1- show HN post

2- let someone else blog about it (or ask for it) and submit to HN

3- post again about the comparison of #1 and #2, with a interesting reflexion (social proof)

I wonder what's coming up next :-)

Social proof is very important. Even subtle aspects can have significant impacts. I think social proof ties in with another area that I think may even be more important: the impression of longevity.

With both my own and others' projects, I've noticed that if you don't give an impression that you've been around a while or that your project/product is in active use or production, you'll find it significantly harder to gain traction. I think this is why the "trick" of using screenshots, videos, and so forth, tends to work well, since people get to see something that, supposedly, is in action, rather than a floaty promise.

If you're launching a podcast, an e-mail newsletter, or something where a sign of activity will boost signups, make sure you get a "few in the bag" and can do your public launch at episode 5, issue 7, or whatever. Likewise, with a business like that described in the post, make sure you can get some early reviews, some testimonials, and some blog posts in the bag so that you look like you're going places, even when you aren't.

It doesn't even have to be someone credible.

Simply puting some images of human faces on your site near the call-to-action button helps. The Facebook widgets that show who has "liked" your site work great for this. Our eyes are drawn to pictures of faces and a group of faces next to a button says "these people tried it, what is wrong with you?"

Some more: * Pictures of faces * A testimonial (one face and one sentance) * A number indicating usage (4,243 downloads today!) * Expert reviews (TechCrunch loved it!)

I don't think this is a good example of social proof in the sense Cialdini referred to in Influence.

Working servers matter more, the page doesn't load for me.