As a commuter the kindle paperwhite was such a step back, the removal of the side buttons effectively prevented you from reading it left handed, I find myself halving to turn the page with my nose if for some reason I have to hold on with my right hand while on the subway.
I've found that there are two things that let me use the Kindle Paperwhite left-handed -- one is that the "back" area of the screen is small, so pressing close to the center with my left thumb, once I've gotten used to the "sweet spot", is very reliable. The other is that it recognizes swiping gestures, so a small swipe with the thumb will also turn the page if my hand is in an awkward position.
That said, I would love to have the physical buttons back -- when the touch screen works, it is okay, but when it decides for some reason that I want to change my font size instead of turning the page, or just decides that I didn't press it, or turns the page twice when I think it didn't register my first touch, I get unaccountably mad.
