While everyone is expecting for Microsoft to dig just a little bit deeper into their pockets (speculations said that $35 per share is a possibility) to try and change Yahoo's mind, Bill Gates is playing it tough, saying they're not raising the bid.
He made this quite clear in an interview with Reuters: "We can afford to make big investments in the engineering and marketing that needs to get done. We will do that with or without Yahoo." In other words, if Yahoo doesn't want the 44.6 bil, they're gonna spend it elsewhere: at least the $19 billion they have in cash.
Of course, we all know that Microsoft is only acting indifference. In fact, if they don't buy Yahoo, they'll have a tough time turning those 19 billion dollars into a web platform that will be a decent competitor to Google; that's why they went unsolicited on Yahoo in the first place.