I'm ex-Yahoo, and I know first hand how utterly rotten the culture was when I left. I once was on a mission to decom a handful of crappy servers running some really crappy code. They were once, in the mists of time, used to perform some tracking on a particular campaign, and were the brain-child of an idiot architect. They cost money to run, so I tried to find who consumed the information they produced. I checked around, and actually found people very helpful - it turns out, no one was using the data, so I could literally have just switched off the servers and no one would care. BUT they were still serving tracking pixels on a number of sites. I then log tickets with all of the properties I could identify asking them to remove the pixels from their pages - "it'll make your page load faster, and it'll mean we can switch these servers off, so save the company some money" (ie. "come on guys, this is a good thing"). I'd say I got about 30% traction - that is, about 30% of the properties involved actually went and did it in the following 6 months. The others just ignored me, and so I suspect those servers are still humming away today - thousands of dollars and a few years later.
So anyway... the point is, there's a long way to travel. There's a huge amount of cultural change required to even make small changes to any of the hundreds of Yahoo properties. From what I hear, Marissa is challenging the property owners to make a big change in 3-6 months - some will make it, some with hack their properties to shreds to make it and some will fail. From there, I guess she knows what she's up against.
I for one do hope they make it. Despite everything, an Internet entirely without Yahoo leaves things a bit too open for the likes of Google and Facebook. Yahoo's got the scale, and they still have a massive, massive user-base. Hopefully they can turn that to their advantage and be a credible player on the Internet. I'm sure people will say "yeah, but Facebook is better" or "Google search is better" or whatever, but that's not the point. Yahoo just needs a few niches that are the best there is (which Flickr could be, if they keep going).
Actually, on Flickr - the mobile App is actually pretty good. I can't admit to using it all that much because I'm a photo-luddite, but the app is quite nice. That's not to say it's perfect, but it's going in the right direction.