Torrentfreak has 'awarded' COD: Black Ops the highest amount of illegal downloads for 2010 - sitting on 4.27 million copies dated to the 26th of December. Keep in mind the game has only been available for not even 2 months.
Other games that made the list were Battlefield: Bad Company 2 with nearly 4 million downloads, Mafia 2 with 3.55 million and Mass Effect 2 with 3.2 million. Obviously this amount looks like a lot and would add up to billions in 'lost sales'.
This is where I don't understand how they can claim lost revenue in piracy... people can buy the game and return it, a store can resell it at near full price and do this more than once with it being OK. The developers build in anti-piracy measures, but when was the last time this worked? Piracy will never stop, of course this does not mean it is not a serious issue - it just means these 'lost revenue' numbers shouldn't be thrown around so easily.