I spent a while figuring out how to stop Crashplan online backup from nailing by connection for everything else that was connected to my Draytek 2920n.

I blogged about it here, including a video of the setup. http://blog.paulgeorge.co.uk/2012/06/11/setting-up-qos-on-draytek-2920n-router-using-dscp/ .

The end result was very good. The backup when running now has very little impact on network speed or latency for other traffic.