TimeWarner Cable (New York City, NY)
Optimum Cable (Upstate New York)
Comcast (North Carolina)
Multiple users, nearly 1/2 of my friend's list contacted me to see if I knew anything. Please report it up.
also, please don't send me the canned answer on NAT settings or clearing system cache. XBoxLive just had a ton of people drop offline and reconnect right back on- most of whom appear to be on the East Coast. The specific ones listed above are from the folks that hit me up or were in my party when it happened.