In a real shocker, this article reports that Microsoft got busted for misleading advertisements. The shock is not that the ads were deceptive -- when one person says using Linux can save you 30%, and Microsoft says it will cost you 500%+, someone is obviously fiddling with the numbers -- but that someone actually called them on it.
Note that this did not happen in the U.S. Although I don't know if the laws are similar -- it may be that in the U.S. it's enough if what you said is factually true, and that was the case here.
The ad apparently claims that Linux running on an IBM Z900 mainframe is more expensive than a 2 CPU Xeon running Windows. Well, no shit, Sherlock -- a Z900 costs about $400,000 in its cheaper, Linux-only configuration. Needless to say you can get a dual Xeon for slightly less than that.