1. Stop all projects that are not contributing to revenue, don't have a path to revenue or aren't contributing to the community.
2. Culture. Focus on the teams building products, reward those doing well, and get rid of those not. Restore work at home for those who do the work, get rid of those who don't. I don't agree with punishing everyone because of a few assholes.
3. Clean up yahoo home page, it is cluttered and too busy. Add a feature like the old iGoogle for those who want the extra stuff on their landing page.
4. Pick a product/service and make it the best thing out there, too much diversity causes fragmentation and a lack of focus and doesn't attract or help you retain talent. This doesn't mean only do 1 thing, just focus to make 1 thing best in class first, then keep moving through each product.
I am sure we have no clue of all the issues on-going within yahoo, but from a product/project and culture standpoint those would be my initial goals.