I think it will do what a netbook should do, but in an elegant way. This means everything on the internet, way better than what the iPhone does. I'm sure it won't replace the MacBook: you can run heavy duty programs on the MacBook, like Photoshop, and you're not going to run Photoshop on a tablet that doesn't have a keyboard or a mouse. It's just impossible. So basically, what I say, is that it will have a full featured Safari that will have Flash (please!!!!) and everything that Safari on your Mac has. Probably an email client and web applications, etc... I imagine a full featured Skype for example, to be a good App to have on it, with a user-facing webcam, etc... I don't imagine it running full OS X: imagine if you could install an OS X application, like Final Cut Pro, and then not be able to run it, since there are many things you simply cannot do without a mouse and a keyboard. If an app is not written with Multi-Touch in mind, it won't work. So it can't run OS X. It can't run iPhone OS either, since that was designed for a smaller device. So the only solution is an OS similar to iPhone OS, but more complicated (not just 9 home screens and voila, but maybe a more complex folder system). I imagine that the tablet won't replace anything, since the iPhone is small (compared to the tablet) so you won't be carrying the tablet around to make phone calls. I also imagine that it can't replace a full featured notebook like the MacBook, since it has not keyboard and mouse, and I don't think it will run full OS X, therefore it cannot do many things that the MacBook can do.
However, there are many people that only use their laptop to access the net on the go, while they have a full featured desktop computer at home. These people don't need their MacBook to be able to run Photoshop or Final Cut Pro, or have a complex folder system with partitions and external hard drives and all that. They only need a small computer that gets them on the net fast, to be able to communicate with people instantly. So in this manner, I believe that the Tablet will compete with Google Chrome OS: it will be very simple, and focused on the internet. I really hope it won't be like the Chrome OS though, as I don't think today's world is prepared for 100% cloud computing just yet. So I think it will be weighted towards the net, but it will also have internal storage to keep apps, movies, music, etc... Just like the iPhone. There would be no point to run the full OS X on it, as OS X has features you can't use on a touchscreen, and it wouldn't be comfortable to use.
So in a nutshell: Tablet = Ultimate internet device, portable, simple, fast but very elegant and aims to replace netbooks.
However, there are many people that only use their laptop to access the net on the go, while they have a full featured desktop computer at home. These people don't need their MacBook to be able to run Photoshop or Final Cut Pro, or have a complex folder system with partitions and external hard drives and all that. They only need a small computer that gets them on the net fast, to be able to communicate with people instantly. So in this manner, I believe that the Tablet will compete with Google Chrome OS: it will be very simple, and focused on the internet. I really hope it won't be like the Chrome OS though, as I don't think today's world is prepared for 100% cloud computing just yet. So I think it will be weighted towards the net, but it will also have internal storage to keep apps, movies, music, etc... Just like the iPhone. There would be no point to run the full OS X on it, as OS X has features you can't use on a touchscreen, and it wouldn't be comfortable to use.
So in a nutshell: Tablet = Ultimate internet device, portable, simple, fast but very elegant and aims to replace netbooks.