Facebook is probably the worst coded app I've got. It's ridiculous how bad it is.
And it progressively gets slower and slower with every update. Although I did notice a slight improvement for the last update that brought it the iOS 7 design.
I'm running an iPhone 4, and for an app like Facebook that's on most people's phones, it's amazing that they don't properly optimize their code. I mean, how is it possible for there to be a delay of several seconds after tapping on a photo to view the full size and comments? And then even dismissing that photo takes several seconds? Never have these problems with Twitter or any other similar social app.
Drives me crazy. As a web developer, I always try to make my code as efficient as possible. Something all types of developers should do if they're thinking of the user experience, which honestly should be above everything else.
Just my two frustrated sense haha.