Kde 4 is completely usable for many people. I am running it with Sidux, a spinoff of Debian, and it is (a) beautiful and (b) runs just fine.

Ubuntu is just fine also.

There are lots of great Linux versions and I have used most of them. The nice thing about Ubuntu is that it is the most popular version of Linux, so if you have any problems with it, extensive help is available.
Mepis is great, Suse is great, they are all great for many, many people. I have Mint installed on the eee pc I'm typing on now, it's great too.

I don't see any big reason why a tablet user would want to run Linux, though. It should work fine with Windows. I'm running Windows 7 on my computers and it works -- let's see if I can find an appropriate adverb -- ah yes -- great.