I honestly think that typing by the book is the best way:
The keyboard seems skewed to the left, but it's not as significant as how it looks in an image. The reason (in my opinion) for this is because of the number row, which is significantly offset. In normal touch typing, you're not mixing a significant amount of numbers in with normal text. If you're typing a large amount of numbers, a normal touch typist will change his/her homerow so that the pointer fingers are on 4 and 7 anyway, so the skewness is not a problem.
Now if you look at some of the in-ward skewed layouts with this in mind:

Now you have the pinky on two different keys (Q, W) and the ring finger on E and middle finger on R (try these, they're uncomfortable).

This one is just weird. I don't have anything really critical to say about it, since I've never tried it, but the 3/4 with one finger, and the fact that you're moving up/down the keyboard in the same directions (left), might be a bit strange.