Summary of the houses' requirements according to the /SortingHat:
Gryffindor Book 1 - "Brave at heart", "daring, nerve and chivalry" Book 4 - "bravest" Book 5 - "bravest and boldest"
Hufflepuff Book 1 - "just and loyal", "patient", "true", "unafraid of toil" Book 4 - "hard workers" Book 5 - "the rest"
Ravenclaw Book 1 - "ready mind", "wit and learning" Book 4 - "cleverest" Book 5 - "sharpest mind"
Slytherin Book 1 - "These cunning folk use any means To achieve their ends." Book 4 - "great ambition" Book 5 - "pure-blood", "of great cunning"
Of them all, Hufflepuff and Slytherin have had the greatest changes ("just and loyal" I could cope with, "hard workers" seems like a cop out and "the rest" is just plain insulting). Actually I guess Slytherin hasn't changed that much besides specifying pure-blood, and it was talking about the original Slytherin at the time.
Of note for fans of Hufflepuff is the order the houses are mentioned in... Book 1 - GHRS Book 4 - GRHS Book 5 - SRGH
Maybe next year, it will be relegated and they'll bring in a more popular house? :) --Kazuhiko