Facebook's future depends on succeeding on mobile phones, as questions about Facebook Home at the company's shareholder meeting once again made clear. Whatever Facebook says about the product now, they sold Home hard, and it has not lived up to its billing.
There's a simple, almost mechanical reason that it's hard for Facebook to be as good and user-satisfying on the phone as it is on the desktop: feedback.
On the desktop, Facebook is a machine designed to make itself better. They hoover up data about how you're using every piece of the service. They A/B (or A/X) test every single part of the user experience. Based on all that feedback, they tweak and tweak and tweak. Then, they do it all over again. Disputes can be settled by simply testing alternatives on a small base of users: may the best data win. And they can do all this quickly because on the web, Facebook can change the code any time they damn well please (although mostly once a week on Tuesdays).
Now, think about the mobile world. Apple and Google control distribution. You have to send your app to them and get it approved. You can't send one app to 0.1 percent of your users and then another app to the other 99.9. You can't iterate on your own schedule. In short, they know less and can do less.