From this perspective, there's no way to decide whether it's a bluff or not. Microsoft is no stranger to hardball tactics, but I seriously doubt that it would turn down a good deal 4 weeks from now just because it sent this letter.

Corporate mergers -- especially when the sides aren't best friends -- are never pretty. My only question is why does Yahoo!'s board think that a giant premium is bad for stockholders? The board's only concern should be getting the best deal possible for the owners (i.e., stockholders).