Comcast and several other ISPs had massive, national outages a couple of days ago due to a routing misconfiguration by Level 3, which is the GIANT physical backbone provider usd by many of the biggie ISPs.
When Level 3 finally made their fix, suddenly my Comcast networking went from basically dead to working very well. However, it seems to me like it has been hiccuping a bit occasionally since then.
I've done all the normal resetting of my cable modem, router and other equipment in my home (firewall, proxy server, etc..) and my service is still slow much of this morning despite paying for their highest tier Internet service.
As I use OpenDNS anyway, that hasn't helped. There's something else going on around here.