Somehow I completely missed this post.
I've read that a lot of people who have the same issues that I do believe the company (CenturyLink) is throttling videos. One comment said that whenever they call to complain that YouTube doesn't work, the person on the other line hangs up as soon as they hear the word "YouTube".
What they are generally looking for are high use. They have enough pipe (in most areas) that they aren't terribly worried about normal users.
What people don't understand is that, under current rules, the carriers pay each other. It's called "peering".
So, if you are hitting servers based out of California from, say, here in GA on comcast...like, lets say youtube's servers...
The traffic will go through your local router (be it one you own or your cable modem...which isn't really a modem, it's a router...), then out to your local Node (probably within a mile or so of your house, but not necessarily), and onto the cable companies infrastructure, with a few hops. At some point it will reach the edge of the lines controlled by your cable company and it will need to "hop" to a different network controlled by someone else.
When it "hops" your cable provider actually PAYS the other provider (Level3, Quest, Verizon, AT&T, whomever...) for that traffic.
So, if some company is running a website, say, based out of California, that is popular with people in NYC, this can lead to quite a bit of expense (not just on their network).
It's not the primary reason ISPs aren't fond of it, but it is a factor.