The sample feature was a surprise when i first got my regular kindle and useful! the dictionary feature was the best, increasing/recalling vocabulary was my main reason for picking up reading again.
as for specifically the pw, the other day i used the xray feature for the first time to help with what is often a problem for me. i have very poor short term memory and if a character has been out of the book for a few chapters i can go back and find the details of his/her first introduction. awesome.
another thing was being able to look up spanish words. i've been trying to learn spanish, i downloaded a spanish elementary reader for kindle and it's so easy to just hit the word and get the english translation! so great.
and before i received my pw i had no idea there was an autowake feature option, that alone is worth getting the pw, i can't begin to tell you how much i deplored using that power button, so awkward, i really don't know how other paperwhite users without a magnet or autoawake cover tolerate that.
the covers wasn't a surprise, but how useful and easier to view has been quite a delight. I have my my 6 main collections in cover view and it's perfect "new", "finished", "over it", "samples" "non-fiction", "stephen king", and it's all i need so far. just loving that.
oh, and i did not have any idea there would be a cloud until i turned on the PW. that is perfect, absolutely awesome. This way i keep my pw materials at a bare minimum. Like i have series of novels but don't keep the future books on the PW. if i've read part 1, i have part 1 in finished, part 2 in "new", and part 3 in the cloud. i keep only 50 unread books on my pw and the rest sit on the cloud til they're ready to come into the mix. great feature.