[Tyrannosaurs]

I suspect it's a reference to the structure of the community, reputation system and permissions that result. The way those three interplay is pretty complex - how you incentivise certain behaviour, unintended side effects and so on. Some of the more interesting bits on the SO blog are Jeff's comments on what they've done, where it's gone wrong and how they've tried to correct it.

On that sense Facebook is very simple as what you can do is almost entirely driven by whether you're friends with someone or not, and the mechanism for becoming friends (or stopping being friends) is straight forward.

Obviously that's a somewhat simplistic view though and ignores little factors such as doing even the simple things with 300 million users is massively complex.