I have a quad core i3750 and an SSD so it was not a problem of CPU useage at all. It was totally just sapping my bandwidth.
I wouldn't be surprised either way. It tends to sap the bandwidth in recent months on my OC'd i7-920 box whenever I have it plugged into Datacenter Internet or FiOS. The older versions of Avast! I know were much lighter overall. Seems to have either taken on bloat or needs some optimizations.