Comcast XFINITY → slow streaming video from xbox live?

for awhile now (past 3 months) video streaming from xbox 360 live has been really terrible - any one else notice this?

I'm talking about the dashboard news stuff, Major's minute, etc. - not the stuff you download and it puts in the pending download list (as far as I can tell)

I wait forever for the green bar to get to the end, then after the video starts, usually it pauses in the middle and needs to buffer some more - really annoying.

Game play (over xbox live) is great, speed tests are great, not having any other problems - any ideas?

I am having the same issues with netflix:
»Comcast throttling Netflix's Instant Watch? Answer: No

I think Comcast is throttling the connection to specific domains and IP addresses... :-\