I'm in both camps. I'm in the Sugar Grove system and some times it is horrid - mostly upstream issues that make my Vonage sound like Darth Vader on quaaludes. Other times, it's pretty good.
Check your cable modem - I had a misbehaving Linksys. Also note that Mediacom is doing radical upgrades to become a VoIP and VOD provider, so some of the wires are duct-taped while they do this.