I believe you're right about the desktop in the office though. The fact that XP is still commonplace in offices goes to show the staying power of the form factor in that setting. I mean, the design of most cubicle farms alone is more suited for desktops than tablets.
What does seem quite plausible is tablet + peripherals - the tablet basically assuming the role of the old mini-tower computer, angled upright on a stand for desktop use, with keyboard and mouse hanging off it. (In fact if you also hung a monitor off it there's no reason you couldn't do that with a regular phone.) I think tablet + dock + keyboard may well become a popular home computer setup in the next few years.
Almost all of my email is sent from my iPad, and I write a lot of email. I send vastly more email from iOS than OSX/XP/W7. I use all four operating systems between my personal and work machines, and prefer iOS for almost all tasks.
Touchscreen typing is weird at first, but, just like using a physical keyboard you start slow and eventually become proficient and comfortable.
I'm not seeing why a tablet is so massively better than a netbook/laptop.
I don't see it going mainstream, or replacing laptops.
I'm not gonna hold a tablet in my hands while I try and use it.
(I spend the vast majority of my time sat on a sofa with a laptop).
A tablet is just irritating because it cant stand up on its own.