There's an interesting piece, "What eBay Could Learn From Craigslist," in the NY Times. The piece contrasts the growth curves and cost structures of the two companies. It implies certain principles could be extracted from the experience of Craigslist that could be applied to other online businesses, specifically eBay in this case.
That may be true in principle, but in practice there won't be another Craiglist.
Why do I say that? The circumstances of Craigslist's growth and development are almost unique. And it would literally be impossible to replicate that success today in any sort of calculated way.
The irony is that Craigslist didn't start with any "roapmap" or plan to be where it is today. And partly for that reason nobody could say: "I'm going to duplicate Craiglist's success" and actually achieve it. Tribe.net has tried and, so far, failed. eBay is trying abroad with Kijiji and might succeed — it remains to be seen.
Craigslist was founded in 1995, when the Internet was in its infancy. It built a very lean business model organically and got to scale in a decade — nobody has the luxury of that much time now. The founders and management of Craigslist scrupulously did not allow the site to be taken over by advertising and preserved the integrity and authenticity of the community. In fact, they guarded the integrity of the community at the short term expense of potential revenues.
In other words, they weren't greedy. And people responded.
The word of mouth and good will that Craiglist developed were based entirely on its intrinsic properties and performance — for employers and ordinary people seeking to buy and sell things.
These and other factors helped build it into the market force (and brand) it is today. Nobody could have predicted it and, literally, nobody intended it. It just happened.