Craigslist has no advertising on their site and doesn't charge for listings except for a few small sections of the site in major metropolitan areas (the funds from which they use for their business expenses). I think it speaks to the state of the bubble we're in that one of the "blue chip" internet companies has a business model of "be an ultra-speculative investment as long as possible." Of course Amazon too, but I'd say Craigslist is a more extreme example.
This is coming from personal experience so take it with a grain of salt:
Craigslist is an insanely valuable source for lead generation in recruiting, and car sales.
I run a recruiting company and craigslist is the best source of applicants by volume and return on investment (cost ($) per applicant).
Having observed them closely, they are not ignorant to this fact.
When specific cities or sections grow more popular they begin charging fees.
Their biggest boon has been a recent change to charge car dealerships 5$ per post. Car dealers pay because only months earlier they were paying for black hat solutions to post for 1-2$ per post.
FWIW, if you ever watched hot girls wanted (a documentary film) you will learn that a lot of "porn stars" were recruited via craiglist. It was a very interesting documentary to see how many people would actually use craiglist to find opportunity.
I was recruited to my first sysadmin/devops/etc. position through craigslist; similarly I encouraged a family member who quickly found a construction engineering position.
How can you say that in response to a comment saying that Craigslist made $335 MILLION and doubled revenue year over year? I mean sure perhaps dispute the underlying facts (they seem rock solid to me) but if making $335,000,000 in revenue is somehow the sign of a bubble then... i don't know what to say.
