Having just read The Website Obesity Crisis[0] I was instantly intrigued by the video loop at the top of this article, so fired up Chrome's network inspector.
Not only is it 6.7Mb, but it's sent using streaming (Status: 206 Partial Content), and for me at least, every time the video reaches the end, it's loaded again, and not from cache.
I didn't actually read the article, but according to Read-o-meter[1] it would take around 18 min, during which time the 15 second video would play 72 times, consuming 482MB of data!
0 - http://idlewords.com/talks/website_obesity.htm#crisis
Edit: Ha, caught out by my own dev setup, ie: disable cache when dev tools is open. My bad, feel free to ignore everything I said :)