No more Mr. Nice Microsoft. Apparently when Microsoft puts $44.6 billion on the line, it really means it, and the company just sent an open letter to Yahoo’s board of directors stating in no uncertain terms that the 62% premium over Yahoo’s closing price on January 31, 2008 was more than fair. The word is now that if Yahoo can’t see that, Microsoft will be compelled to take its case "directly to [Yahoo’s] shareholders." Microsoft is giving Yahoo three weeks, and then promises to try and start a proxy contest to elect an alternative set of directors to the board. This is about to get good.