Microsoft must be broken up into at least 10 companies. Otherwise, this nation needs to stop pretending any sort of "market forces" dictate our economy or corporate ability to consolidate.
The hard part is finding an unbiased economic framework for understanding conglomerates like Microsoft. I suspect that if we built such a thing it would necessarily take down more than the tech giants. The media conglomerates (Disney, Warner, etc...), and more importantly, the financial giants. You have hurricane-strength headwinds to make something like this happen.
I'm not saying it shouldn't, I'm saying it's very difficult.