Are there any super nodes in the network? Similar to BitTorrent trackers. Or are all peers equal in ability and importance?
There is a node that will relay all transactions, regardless of whether a fee is paid:


http://en.bitcoin.it/wiki/Free_transaction_relay_policy


There are well-connected nodes that are recommended for use by merchants to avoid risk to a race attack.  Some of them have inbound connection whitelists so as to lessen the risk of intentional address list poisoning.