What I've noticed about 0.8.1 (and 0.8) when analyzing traffic with jnettop (was the quickest thing I had handy) is that a peer can ask for blocks and bitcoind will happily send them as fast as it possibly can. If that peer asks for a large range (500 at a time) bitcoind will happily saturate your entire uplink to deliver those block requests.

I've seen single peers pulling 250KB/sec through my DSL uplink, absolutely destroying anything else I'm trying to do. Restarting bitcoind disconnects that peer and they move onto another peer, which is why it seems stable again for a while after restarting. Eventually you get another greedy peer and the cycle repeats.

There is no built in throttling. You'll have to manually figure out a way to do QoS/throttling so it doesn't kill your link.