It's the pure definition of 'nitpicking!'
A lot of those changes are for cinematic effect and (in my opinion) serve to make a little more sense in certain places. One example I can think of is on Carhadras, where (in the book) Boromir declares that 'there is a foul voice on the air.' Having Legolas hear it in the movie makes a bit more sense as Elf hearing is a hell of a lot sharper than human hearing and thus begs the question of 'well, if Boromir heard it why didn't Legolas?'
But that's just me! Personally, I think that Jackson did a superb job and the legions of LOTR nitpickers should be happy that the trilogy HAS been made in some form and to such wide acclaim. It may not be the version that they want to see, but let's be honest here: How filmable is FOTR with all the stuff from the book put in? That is, 17years gap between the birthday party and Gandalf's return, Tom Bombadil etc etc. For starters it would run to a ludicrous time and quite frankly be boring as hell for the first three hours or so. The audience will long have left by then.
