I hate the fantasy film genre. Hate it with an effin' passion. I can't suspend logic and embrace disbelief long enough to enjoy most fantasy films, for some reason. (Unless the star of the flick wears a cape or spins webs on which he can swing, that is...).That dovetails nicely with a couple of other posts I found dealing with when a movie or TV show gets something so wrong that it ruins the moment (along those lines, this site catalogs bad science on screen). The posts and, particularly, the comments are an interesting read. Absorbing fiction, to a certain extent, is all about suspension of disbelief. Sci-fi and fantasy require more of it, but internal inconsistencies can really blow the mood.
In some ways, it depends on how critical the error is to the work. I can turn off the legal nit pickers mind when I watch Law & Order and ignore the procedural weirdnesses that never happen in the real world (judges deciding motions while walking in the hallway with counsel? without the defendant present? or a court reporter? complete horse shit). But if the big twist at the end gets the law way wrong, I can't let it go.
Whether you can overlook the flaws also comes down to how much you care about the characters and what's happening to them. For instance, last night I watched The Deer Hunter, which includes two scenes where the main characters go hunting in the mountains. They're from around Pittsburgh, but the mountains clearly are the Rockies - indeed, those scenes were shot in Washington State (with non-native deer, to boot!). I noticed because I was already disengaged with the film (it's entirely too fracking long). Had I been more engrossed in the characters and what they were doing, I probably wouldn't have noticed it.
I think the bottom line is that if you go into a fictional experience with the intention of nit picking its flaws you can and it will ruin it for you (and those around you, probably). Don't sweat the details! Save your ire for the really colossal screw ups.