I was skeptical that they would reach their goal, but you have to give credit to Dalton aside from the release of the alpha and support from some big names in tech. The blog posts written throughout were all unique and interesting (great Hacker News titles) and the PR was orchestrated extremely well in my opinion. Kudos!
You really have to give credit to Airbnb - this series has been star studded and I imagine it does a lot to keep their recruiting pipeline flush. They're not pioneering some novel technologies or working on an everyday utility, but they have managed to create a great aura around their engineering group. Kudos to the team for yet another atypical marketing success!