Tor reputation system

[Alok Mishra]

I was looking at the design paper on Tor. I was thinking that one 
problem with malicious node might be that they would advertise their 
services and when the directory servers  attempt to connect to them they 
reply fine but any other request is totally ignored. Since directory 
servers can't afford to  try passing traffic through so many nodes to 
ensure that they are functional, do we need some kind of a reputation 
mechanism that will collect evidence from each of the OPs that 
successfully (or not) can complete their transaction.