uTorrent lets you schedule speed limits for different times of the week (hour granularity, I believe). You can even tell uTorrent to stop all transfers during peak usage periods. Global max connections is another way to limit your network impact as chmod mentions, and you can also decrease the number of active (either seeding or downloading) torrents allowed at one time. I also like to set my per-torrent connection limit low, but AFAIK uTorrent won't let you set a default per-torrent max connection count or UL/DL speed, unfortunately.
Additionally, uTorrent has a web API (part of the WebUI, which you have to manually enable) which you can use to adjust network & torrent settings like max UL/DL rate. So you might be able to script a macro that automatically tells your uTorrent client to throttle down when your browser is opened or when you get some type of signal from the network that there's heavy usage going on when certain high QoS services are in use (e.g. VoIP, video streaming, etc.). But you'd need a way for your router to signal your computer or directly use the web API to throttle down your uTorrent transfers.
Another simple way to do this, if your router supports it, is to just set the QoS of your uTorrent port to low priority while setting your other network services' standard ports to high priority (here's a detailed guide on setting it up on DD-WRT). However, many people have their bitTorrent client cycle through random ports because of traffic shaping attempts by ISPs. And if you, say, set port 80 traffic to high priority, this could decrease the effectiveness of your router's default QoS scheduling.
