Only when pushed. Normally I don't complain that much when a movie changes something about a series I love, mainly because I don't care. If the franchise is explicitly multi-media I'd be concerned about it having changed something, but if the movies/books/games or whatever are supposed to be their own story then I don't see anything wrong with making changes where you have to. A good example would be something like Batman. Trying to do a direct adaptation of 70 years of comic book history into movie format is pointless, so what you have to do is take the character and tell your own story with him, which is why no matter how different Batman/Bruce Wayne is from the comic books, I don't complain.
However, if someone were to ask me 'do you think the movies do a good job' or something similar, I would list changes from the comic books as points of concern if and only if i thought the changes missed the point of the comic book. Changing the ending of Wanted, or Kickass for example, changes the entire dynamic and feel of the story. I may not like the original comic books, but at least I got what they were trying to say. Changing them and thus changing the point therefore makes me concerned.
Making Batman slightly less insane and Bruce Wayne more than just a millionaire playboy is not a complete game changing adjustment. As long as Batman fights for justice because his parents were shot, but he doesn't murder in the doing so, then the moral of Batman remains. It's why I don't like the ending to Batman Begins. For the Batman I know, not saving someone has just as much a negative effect for him as outright killing them. Dark Victory, Long Halloween, Lovers and Madmen, Face the Face, Under the Red Hood there are so many examples of times when Batman has gone to extreme lengths to save even the most heinous of murderers because the line is drawn where he stops trying to save people. Batman would never let Ra's Al Ghul die on that train.
Contrast with Watchmen. I don't care that the ending changed the exact event which stopped the war. The point of the book was that the war had to be stopped by extreme measures, what those extreme measures are doesn't matter.
That would be where I draw the line at 'that guy' being just another rabid fanboy. When it doesn't matter, because the original message is unchanged, let it go.