We will know tomorrow. http://read.bi/QtH34U
My prediction: Yahoo rebuilds their local search product with user reviews etc. to rival Yelp and adds it to their Bing feed to go after the mobile search market with something distinct and unique from Bing while still using Bing web search. Plus they redesign their SERPS .
Surprise, surprise. She's going after mobile (...like everybody and his dog). Still, it's still an emerging marketplace and there isn't a truly dominant player as of yet, so it might be possible for Y to leapfrog from it's poor position in desktop marketshare.
http://www.businessinsider.com/here-is-the-plan-marissa-mayer-just-announced-to-yahoo-employees-2012-9
http://searchenginewatch.com/article/2208508/Marissa-Mayers-Big-Plans-for-Yahoo-Grow-Mobile-Partnerships-Scale
Mayer said that Yahoo will do more "acqui-hires," where it buys small companies not for their products, but for their engineering talent.
I am not expert, and have not followed that closely, but isn't this exactly what they have done historically?
The resulting announcement was so vague as to be almost worthless. Still, Yahoo needs to stay in there creating apps that keep their services viable and accessible to the mobile market. Frankly just completing what they start would do wonders.