Disappointed with Jelly Bean
I'm a bit disappointed in the Jelly Bean upgrade. Project Butter and Google Now are pretty nice, but they're not the kinds of things I was hoping to see to bring Android tablets in particular to the next level. Project Butter is really just playing catch up with iOS, and Google Now doesn't do anything to address the fundamental usability issues with Android tablets. I wanted to see more forward thinking about use cases and integration with laptop/desktop usage ala Windows 8. Two features jump out as killer additions that would really make Android tablets great.
This is the main thing that frustrates me with tablets. Even with the dedicated multi-tasking button, there are some tasks that are just painful on Android because you need to rapidly switch between multiple apps.
I was really hoping to see something like Onskreen's Cornerstone app or the Windows 8 split screen. Having one tablet-sized app and one or more phone-sized apps seems like a great solution to me, and the Android Fragments API is a good starting point for this feature.
Multiple User Profiles
Phones are very personal devices, but tablets are the perfect size for sharing. I don't want to buy his and hers Asus Transformer Pads Infinity and try to remember which is which; I want to get just one and leave it on the coffee table at home. Pick it up, tap your picture, and you're in with all your own settings. Some individual apps do this currently; the latest gmail makes it easy to switch between mail accounts, but most apps don't, including most Google apps.
Essentially, something like SwitchMe only built in to the OS.
These two features would bring Android computing a lot closer to the post PC era, by implementing some of the key features we take for granted in our laptops and desktop PCs, but haven't been demanding on mobile yet. It would set up Android as a nice counterpoint to both iOS and Windows 8. Maybe in Key Lime Pie?