[andycroll]

I'd say _that_ is a hell of an assumption. The travel industry depends hugely on efficient PPC advertising with companies at any serious size.

This has been true of all three travel startups I've worked at. AirBnb may well have great brand recognition but I'd be amazed if they can acquire customers for zero.

[GFischer]

Anecdotally, they do have some very strong direct/organic traffic based on word of mouth and brand awareness (that doesn't mean zero CAC of course)

I don't know where this derives its data from, but it seems to support it:

http://www.similarweb.com/website/airbnb.com#overview