I always have moments on which I get the urge to read them again, but for some reason I never did.
I think it's because it will never be the same again. Like, reading the books for the first time was totally epic and will remain an awesome memory. Especially reading the last few chapters of DH was sooo exciting, although I was rather sad when I finished it. Simply because of knowing that 'that was it, it's over'.
I especially loved that chapter in which...nevermind I won't spoil it

... or oh well (*small, very small spoiler incoming, close your eyes!*), in which everything makes sense all of a sudden...the chapter involving the life memory of a certain someone...
There, that was pretty subtle, I don't think that really spoiled anything, feel free to remove it though.