An interesting explanation of various issues that the Facebook Mobile Dev team ran into while building their mobile app, here.
Some of the main issues that they ran into were:
Lack of Developer Tools
This is an issue that quite a few developers and and UX people probably share. I know I have run into issues when reaching the point in building a website where compatibility checks are performed across a variety of browsers. If something doesn't line up, I need to access some inspector to check out what may be wrong. Can't do that with mobile, yet. Of course I'm fairly sure they have the desire for more tools.
Memory Issues
Following the initial theme, they wish there were more dev tools for memory. Pretty useful for the infinite scroll technique, that will blow up your buffer like what.
FPS
They want a tool for measuring on frames per second, pretty cool idea actually. Would be nice to have one system wide.
Scrolling
They go into a lot more detail on this one. There are a few problems that they have with the quality and put forth some questions for the current API. Mentioning of events during scroll, performance via GPU, standard momentum to just mention a few.
GPU
Would like a better API for hardware acceleration via the GPU.
I would highly recommend checking out the actual writeup, it goes into significantly more detail. It's a cool little summation of their attempt to push an app powered via HTML5 and JavaScript. While it may have not really worked out as planned, it is a great test of the capabilities of the young standard. Hope that the things learned from this foray help make for some great progress forward.