What do these liquidity providers do exactly?
People are constantly running the mixer. That's all. Only A couple of weeks ago, Evan made it so that, if you're available for mixing, and you run liquidityprovider=1 in your conf file, you won't mix unless someone needs you to. That is, you won't start mixing sessions, just join them. This way, we don't sit around mixing with each other, and unnecessarily bloat the block chain. But there are at least 6 people running liquidity providers according to the proposal that was approved, and that should give plenty of deviation so that mixes should be very good. Plus there are others who just do it to be helpful. Always do at least 2, better >5

Hmmmm.... Isn't it dangerous to have to rely on only 6 people who are available for mixing all the time?
I guess that these people have the logs of the mixing. If they collude, they can know which mixing input is associated with a certain mixing output.