I also use Comcast and have periods where I will suffer lag issues and rubber banding that causes the game to be hard to play while doing anything combat related. It seems to run more for me during weekends and comes and goes. However I do know this, when it happens it happens for several hours at a time and my girl who is sitting 5 feet from me playing a different MMO on the same connection has NO lag or connection issues to speak of the whole time.

Under normal conditions we can both play, stream video and/or run downloads with no issues, however once the game decides it wants to start lagging it doesn't matter how much I tone down the other activity as the problem still continues.