My father has a Kindle, and has been using it every day since January of this year. He loves it. He was looking at both the Nook and Kindle before he made the decision on the latter, and doesn't seem to regret it. Recently, after using his for an hour or so and then checking the Nook out in the store, I decided on the Nook (and was gifted one shortly after by my girlfriend). I haven't seen much of a difference in the size of the selection of eBooks offered on Amazon and Barnes and Noble. I spend equal amounts of money in both stores, but at least I have a membership to B&N, if that helps any.
While the Nook's touchpad isn't the best, it does what it's supposed to. I don't find it to be a huge deal, considering if I need faster access to any kind of information outside of the book that I'm reading, my computer or iPhone is always within reach (probably the main reason why owning a MacBook and an iPhone negate any reasoning to own an iPad). However, I did like that this small touchpad freed up more "real estate" for the screen, instead of having the Kindle's keypad. My father doesn't mind this, and seemed puzzled why I wouldn't need to hold a keyboard while reading my books..
As far as the button placement for page-turning goes, it seemed to me it was a case of "six on one, half a dozen the other." The buttons functioned as their counterparts; they turned the page when pressed.
Now, as I don't own a Kindle myself, I'm not sure if it has a microSD expansion slot like the Nook, or if it has replaceable/serviceable batteries. Really, the Nook vs Kindle arguement comes down to a matter of personal preference. IMO the iPad is certainly a cool gadget, but I think it would make a terrible eReader. Also, don't forget that Sony makes a reader as well.