I was watching a video on another sharing site the other day and that kept popping up a new advert every 1 min so you had to keep clicking on the x or put up with only seeing 1/4 of the picture.
I expect a lot more suckage as even the bigger sites need to extract more money from views. It's funny that Chris Anderson's new book "Free" (which is basically the second coming of the 'new economy' bs from the first .com bubble) should come out just as online businesses are getting a lot more realistic about what they can and can't give away and how the ones that are offering services for free are realising that they can't give the kind of quality Google used to indefinitely.
Evernote put nagging adverts into it's client for non-paying users a few versions back. Spotify seems great at first, but the more you listen to it, the more frequent and longer the adverts are (and I have counted them, I'm not just imagining it!). More and more .coms are shuttering free services before they go bust and switching to different projects.