I've noticed a similar problem that started about the same time (last Sunday,the 7th). It started with Yahoo when ads weren't blocked in the mail list and some began appearing in the margins.
Then a day or so later it had spread to You Tube, with video ads being injected into running programs!
Today (the 13th) it had spread to other sites, with ads interpolated in text in stories, banners at the top of the screen, and lots of ads on the right margin. It's as though I don't have Adblock Plus activated at all (but it says I do).
I reported these every day now for about 5 days, and gave my e-mail address, but I've heard nothing and the problem is getting worse! Has Adblock Plus been hacked or what?