UPDATE: The relay network has been updated to use Bitcoin FIBRE - you can find th enew instructions to peer with it at http://bitcoinfibre.org/public-network.html.

Many of you have likely seen the recent discussions on the P2Pool thread and the post on the foundation blog about the relay network.

It exists as a way for pool operators (and all miners, though not hashers) to get their blocks relayed quickly across a separate network both as a backup to the P2P network and as a quicker way to get the latest blocks as it skips relaying transactions which have already been seen. Thus, if you're a miner anywhere from a small p2pool miner to a large pool, you should be running one of the relay network clients.

You can see more information about its original goals and its original announcement here

You can find the latest information at http://bitcoinrelaynetwork.org/