The BitTorrent client could show: number of complete and incomplete peers in the network, number of peers we're connected to and have accepted connections from (and details about them, like individual transfer rates, and average rates from them in the past), which blocks we're currently working on and progress within them, and a graphical display of which blocks have been downloaded and which blocks we've served most often (a bar with different colours).
The Snark client implements some of these ideas.