I think the question's off. I'm not sure identifying all one can do with a KF is really useful, so much as identifying what one *wants* to do with a KF. Once I did that, the KF became the useful toy it is, without any delusions of having a tablet. I don't have a tablet. I have a toy that allows me to download games I like, read books, see movies and listen to music, as well as catch up on tweets and e-mail. It's not a computer, it's an entertainment adjunct for me.
If, on the other hand, you're not satisfied with the Amazon eco-system (and I could see many reasons why it might not satisfy entirely), and you want to have a tablet to give you the open-source flexibility (which, for me, requires more work than I have patience or time for), or potentially a replacement for your laptop, you don't want a KF. Invest in a refurbished top-of-the line tablet with more muscle than the KF, and optimize/configure it as you see fit.
Anyhow - after owning and returning an iPad, which I deemed useless for the price, and borrowing a Toshiba Android tablet for a few weeks (nicer, but still - for the price), I realized the limited use I really wanted out of a tablet and the KF fit right in to my specs.
I have a beast of a smart phone (Galaxy S2), which can do all the photography, updates, calculations, etc etc I might get out of a more expensive tablet, and the KF, which is an easy to use toy.