It’s already well known that Comcast interferes with bittorrent traffic but what is less known is that their measures also take out other legitimate applications, such as iChat AV.
The trouble with interfering with some traffic is that you then have to defend why you don’t interfere with other types of traffic, of a more pernicious nature. One would think Comcast would save more money by building a decent network and defending its common-carrier status.