At the crux is the question of how Microsoft will fare in the search landscape sans Yahoo, particularly after five years (and billions of dollars) of investment.
"Microsoft hasn't even been able to challenge Yahoo (still in low double-digits), much less Google," Sullivan says. "Maybe Yahoo will pull off being the number two in search and online advertising that Microsoft wants to be, while Microsoft becomes weaker as the foundations of what it's built on: the Windows operating system and software, begin to erode in the face of free apps."