Remember guys,
Statistical analysis will reveal you if the first and last node you connect to are compromised/subpoenad. If you use six different proxy servers, the only thing a government or adversary needs access to to find out that you pwned a machine is the first proxy you connect to and the last proxy you connect to. Using statistics and packet analysis, they can figure out those two are connected without having to lead the chain down whatever proxies were in the middle.
Three servers between you and a client are pretty much as much as you want. The ones in between your first and last proxy server only serve to make it harder to tell that those two at the ends were used in the same connection. Anything beyond that really only serves to make your internet slower.