I assume they could effortlessly ramp to $1B if that estimate is semi-close. It would cost virtually nothing to add more paid markets and services; maybe allow the gravity algo to be tweaked.

Figure very low costs for a site like that you could make your money back in 5-6 years; which is insane at that scale. I bet if they put it up for sale for $3B it would be sold by the end of the week

At least 10x their yearly profit? What other investment provides a consistent 10% yearly return on the scale we're talking about?

At P/E ratio of 5, you literally just wait 5 years and you've just made as much as your initial investment.

Given craigslist has been around for 20 years I think it's fair to assume they could take an upwards of 5 years to unseat. Even Myspace continues on to this day.

A p/e of 5 is NOT reasonable. Has everyone gone mad? Blue chips run at about 20.

Therefore I would pay 10B for craigslist in a heartbeat. I could probably even get a bank to loan me the money.