why aren't the chinese or someone with half a brain replicating what FB does? what exactly is the barrier to entry here? to trade at such a high multiple of earnings would suggest that NO ONE else can do what FB does and will not be able to do that in the next 145 years.
The Chinese made Ren Ren which is similar to Facebook. One barrier to entry is creating an incredibly robust infrastructure for the site, which is much harder than most people think. That's partially why the statement "anyone can build the next Facebook" is incorrect. People got tired of Myspace, not only because it was lame but because the site was not build to accommodate updates and growth as well as it should have been. Another barrier to entry is simply the ubiquitous status that Facebook holds in society. Everything links back to Facebook now and for the foreseeable future.