We can do much better with the Tablet UI
At its most basic, the user interface of today's mobile operating systems are the same. You tap a grid or list of icons which then immerses you in the application. When you are done, you exit out and return to the grid or list. This paradigm was remarkably helpful in teaching people how to use a smartphone during the transition away from flip phones. It is also a remarkably effective way of interacting with a phone's smaller display. With that smaller screen, you want the app to fill as much of the display as possible.
But, when the screen is drastically increased, as with a tablet's, the paradigm is no longer effective. On today's operating systems, the larger display just shows you more icons and a better version of the app that can show you more content. The single task model of computing is simple, but the operating system does not take advantage of the larger screen real estate given to it. One should be able to multitask with that extra display.
This is especially true for iOS in which the tablet user interface is fundamentally the same as the phone UI. For iOS, there are many beautiful tablet apps which take advantage of the display, but you are still limited to, more or less, do one thing at a time.
For Android the user interface is the same, but the number of actually good tablet apps is still very low. There is no real difference in experiencing Android on a phone than on a tablet. The most obvious example is the official Twitter app which looks exactly the same on a phone as it does on a tablet, albeit more stretched out.
Simultaneously being able to interact with Gmail, Calendar, and my Reminders app.
Though, Android has a fix to the issue of being able to only do one thing at a time: widgets. Widgets placed on the homescreen act as a way to interact with different apps without going into any particular one. It allows you to multitask and see much more. But according to research done by HTC, the average user does not use widgets and barely adds, deletes, or rearranges them from the day they get their phone. It's a stop closer to the right UI of a tablet, but ultimately pointless as the average user does not understand it. Windows Phone has the same widget paradigm, but in the form of live tiles.
Through Android's ability to customize the OS arises another fix to the single task model of computing. This fix comes in the form of Chat Heads as created by Facebook. Chat Heads allow one to chat with somebody easily and without much interruption to what you are currently doing. Talking with people should not require you to go into a whole other app, rather it should be able to be done quickly and spontaneously. While you wait for someone's response, you should be able to do another task like reading tweets or surfing the web. The Paranoid Android ROM allows any notification to be turned into a chat head. Thus, one can be doing something else while waiting for a response to say a text or tweet.
Chat Heads come very close to taking advantage of a tablet's display, but I believe the correct paradigm of tablet computing is in Windows 8's ability to snap apps. Snap allows you to dock an app so that it take up either a third or two-thirds of this screen and allows you to snap a second app into the remaining space. One can effortlessly do two tasks at the same time. Some apps, like Twitter clients, don’t need to take up the entire screen of your tablet to provide a good experience.
I believe this UI approach to multitasking is much more efficient for tablets. The extra screen size allows you to do more than one thing, it allows you to multitask. I hope Apple and Google take note. Adopting Microsoft's approach wouldn't be more complicated for the user, but rather will allow the user to better use and take advantage of his or her tablet.
Plus, it would hasten the death of the traditional laptop. On laptops, you are rarely just doing one thing at a time. You have multiple tabs open in Chrome, you're listening to music in iTunes, editing and uploading photos, etc. Imagine if you could do those things on something much more portable. You could be more productive in more places. With chips becoming more powerful and more efficient the technical arguments to implementing this way of multitasking are squashed. Look at Haswell and the upcoming wave of Windows 8 ultraportables and tablets.
I believe the experience of using a tablet can get much better. Imagine what ideas and flourishes Apple and Google can add to the conversation. We are three years into the tablet revolution and we have not fully flushed out what the correct UI's of tablets should be, nor do we understand their full potential.