Microsoft and others have tried this before, but never with an OS like Windows 8 so not really fair to compare. I think they have a huge opportunity over Apple at the moment, they have unified the interfaces on all their devices, and familiarity and application sharing will be beneficial overall for the ecosystem. So long as the interface is good enough for a tablet OS then they are ahead in terms of strategic technical direction of unifying the platforms. This is something Apple probably won't or possibly can't do between iPad, Phone and Desktop. The new hardware out there is simply amazing, computers no longer need to have a keyboard, but the keyboard can be used to make an ultra book, or extend the battery life of the removable screen/tablet.
What Microsoft has done is not to obsolete iPad, but provide a very good alternative to the iPad, with many hardware solutions to pick and choose from.
I have upgraded my primary laptop to Windows 8, an older laptop and have been using Surface RT over the weekend. The more I use it the more I am liking it, and can't imagine going back to Windows 7 for my own personal use. My review of the Surface RT would definitely be more positive from the Verge's review in many ways. I have some complaints on some of the apps like Music app seems a bit buggy on Surface, but I'm sure they will fix that over time. My biggest complaint is no native app for Amazon music/video, hopefully they will add that. I can still use cloud player but I would prefer to have a native app like they have on the Fire.
As a test I handed Surface to my Wife with the Travel application open which is a very nice application. She didn't even need to be told how to use the thing, it was so natural, and intuitive. Internet explorer is really well done for touch, not a single hint of chrome on the screen, just text unless you use some simple gestures to pull up address bar and quick launch icons.