Maybe I'm in the minority here, but I don't think "fixing" Yahoo ought to be as difficult as people make it seem.I worked for a semi-dysfunctional semiconductor company and so I think I have some perspective on what it takes to "fix" a company like Yahoo.
I think the biggest reason a company becomes like Yahoo has less to do with senior management and more to do with the fact that the company is filled with low to mediocre quality middle managers and employees. Mediocre managers aren't very good at their job, so it seems like they make up by playing politics. Once politics is rampant, what gets done is not what works the best, but what helps you or your team get ahead in the political game. At this point you start bleeding talent because good people prefer not to work in an irrational workplace. You also lose the focus and initiative you need to keep a successful product successful.
The worst part is that there's nothing you can really do to fix this. You can try to fire the bottom 10%, but if you only have a problem with the bottom 10%, you're not yahoo. You probably need to fire the bottom 50%, but then you wouldn't have enough personnel to keep all your assets going AND some of that 50% would also be good employees who lost out in the last edition the political olympic games.
Any well-intentioned change in process or product focus by top-management will also inevitable morph into something completely different thanks to your low-quality middle managers who won't understand what you're trying to do, but will understand that they need to step up the politics to keep their jobs.
I guess the point of my rant is that a big company is like an emergent system and you can't really fix a dysfunctional emergent system by changing a small number of things that are part of that system.