Why do you think all the TV networks have embraced putting TV shows online? Because they realize they can put ads on the stream and the user has to sit through them (or go to the bathroom). Either way, they can't fast forward through them like they can on a DVR.
...except that in my case, I block the paths to the ad-content streams. You know what happens? Video stream loads, html5/flash then goes to the "insert ad" code, gets no response, and moves on to the next queued stream, until the next in the queue is the non-ad video. This means that where others get ads, I get about 3 seconds of spinners. I could probably write a greasemonkey script that would flat-out scrub references to those streams from the code so that playback is seamless -- AdBlockPlus, Ghostery and NoScript plugins already do that for me in some situations. I didn't even realize YouTube had ads until I was shoulder surfing someone's iPad....