I noticed some lag on the Tuesday and Wednesday but have to say it seems to be occuring less and less. I have to say I quite like it but am yet undecided if I prefer it over MW2, I have to get to know the maps better in wultiplayer. Yes there are definitely hackers already which I find really sad, they are easy to find and download on line and they always seem to be able to bypass the Steam anti cheating monitor.
Im loving the single player to, there is so much work goes into the Call of Duty games script and story wise. Loving the acting voices too.