[eps]

> would be able to MITM any conversation

Sure, in theory. In practice, eavsdropping on two Skype users required presence on a network route between the callers, which might have been entirely in some random country's Internet segment.

[pieter]

Not really -- the directory server can just direct a user to connect to a MITM server. There's no need to control the entire network, you only need access to Skype's servers.