"Do not rely on the ratings blindly - since the cost of entry into the web of trust is only one positive rating, it is not impossible for a scammer to infiltrate the system, and then create a bunch of bogus accounts who all inter-rate each other. Talk to people on #bitcoin-otc first, make sure they are familiar with the person you're about to trade with, have traded with him successfully in the past, etc"
So it's about knowing people actually, and the ratings only make sense within the circle that know each other. I see similarities with my idea Credit networks based on real-world relationships. I wonder how many in the WoT know each other's real-world identities?
Well some, like MP, actually operate under their own identity, rather than some pseudonym. Plenty others use a pseudonym but have their identity clearly linked to it one step removed (such as on github, some personal blog, etc). I would imagine most people know each other at least to some degree behind the scenes. Then again this "have met IRL" is not the end-all, be-all - as pirate's Vegas show illustrates.