The current #2 on Videosift http://www.videosift.com/video/Fox-News-Declares-War-on-Canada
It has a fair amount of comments so there are a lot of avatars loaded each time this video is clicked.
I saved all the avatars to my computer and the cumulative size of the avatars was 132 KB. This doesn't sound like a lot, but it's probably responsible for a large part of the bandwidth used to provide this page to the user. Especially if you consider that most of the Sift's design is based on code and not graphics. Importantly the top videos usually have long comment threads, thus a lot of avatars, and the top videos are also those most watched.
So my point is this: The Videosift can save a lot of money on bandwidth if they only allow avatar images which are externally stored, like on your own webspace.
Or you could upload a maybe bigger and better avatar to VideoSift for a nice price. People must pay much extra if they want to buy the option of animated avatars