Improving the work environment, as only one example.

Probably the biggest improvement: getting the point across to a huge organization that they're not content just sitting back with things as usual. Yahoo had become the behemoth that plodded along, one step after another. Someone needed to come in and whip the company into shape, from the Veeps on down. If nothing else, she's woken the company up. And that right there is something big.

For what it's worth, their iOS weather app is absolutely fantastic and I believe is now being aped or outright used by Apple in iOS7.

Small things, but it is a very nice user experience if what you're after is the weather.

Sportacular for iOS is also great. Provides no-nonsense scores and news for almost every sport (I mainly follow basketball, tennis and soccer, though). It is a much better interface than what Yahoo's own web equivalent (sports.yahoo.com) has become.