iTunes is what Apple was right before steve came back: One entity trying to do too many things. The solution is either 1. to remove massive amounts of features and stick to the bare essentials like Steve did, or 2. split the entity up into multiple parts and let each worthless part die on its own accord. I'd say #2 is the likely option.
Give us a Music app that's really great at playing music. Give us a Photos app (iPhoto) that's really great at displaying photos. Give us a Movies app that's really great at playing movies, and so on. When we want to do one of those things, going to an all-in-one app just confronts us with an endless supply of things we DON'T want to do, and makes getting to what we're after much harder. I think this may even be an addition to ML by the time it's out for sale.
EDIT: And as an addition, do a little of the opposite with the App stores. There's no reason for them to be separate stores when many of the apps on them are the same. You could even make the apps ARM/Intel Universals, paired with multiple NIBs for the three different UIs (iPad/iPhone/Mac) like is done with iPhone/iPad universal apps.
