Good question. A "qualities" list might be useful. Needn't hit on all cylinders, but most/many would be a positive.
Someone with experience in:
- Software and/or hardware experience, obviously.
- International regulatory affairs. Microsoft continues to face (and initiate) anti-trust issues in the US, EU, and elsewhere.
- Deep corporate/institutional relations. If not from the inside, then on the "working with" basis. Extant large enterprise sales are still a large part of Microsoft's domain.
- Mobile. Devices, form-factors, interfaces, applications, future directions. It's clearly an important space, though I think Microsoft are a bit too obsessed with winning-at-all-cost (and failing as a consequence) in it.
- Entertainment. One of the current growth avenues (and one posited end-game for Microsoft) is in the games and content consumption space. It's one of the few areas in which Microsoft are arguably executing well, especially compared to major stumbles on competitors' (viz: Sony) part.
- Financial services/products. Even in enterprises which are otherwise Microsoft-free, the one standout is typically the CFO or bookkeeper's Windows box running Quickbooks, or other financial software.
Additionally, addressing Microsoft's traditional failing points would be helpful. Platform security against viruses, malware, etc. Hostile industry relations (Microsoft rabidly treats all peers as enemies, and has since very early times). General consumer trust. "Cool" factor (you've got to earn it though). A revenue model that can survive loss of software licensing / corporate sales / OEM. Chronic UI / usability issues -- very hard to address without pissing of existing customers. Relations with the Free Software community. As Bill Joy observed, "innovation happens elsewhere", and as Microsoft is knocked off its king-of-the-hill perch, it should find that being able to share and integrate software really is a good thing.
Things I'm not mentioning: Most prominantly, cloud computing. While I think it will be a part of Microsoft's future, I think it will emerge as something the support out of addressing much of the above, rather than as a primary focus.
I don't know enough industry personalities to put a finger on who's a good fit, but it might be fun to see who comes up.
