Tablets are definitely the way of the future, but my guess is that the keyborad and mouse will soon enter into a happy marriage with them. The problem right now is that it's very hard to make a lightweight, desirable tablet which has specs comparable to a decent PC.
That will change, and when it does, people will buy a tablet that comes with a keyboard and mouse, plug them in, and use it just as they would a desktop computer. Then when they head out later on, they'll unplug it and bring their tablet with them. Or, they'll have extremely portable (possibly fabric-based) versions of those devices. They'll have the best of both worlds.
There are many people out there who use their computers primarily to browse the internet, listen to music/watch films, and write things (emails, tweets, facebook updates, essays etc). They don't want a big home computer and a fairly heavy laptop. They want something simple, portable and functional.
I agree that tablets are currently not capable of replacing traditional computers. I certainly won't be getting one yet. But I can definitely see a day when they'll make sense.