Factual error: In the very last scene, Mikael and Erika get into a taxi and head off. This is on Bastugatan in Stockholm, and they are heading west. Bastugatan is a one-way road, and you can only go east. (Go to Bastugatan 14, Stockholm, Sverige and look west, the scene is very distinctive, as is the Do Not Enter sign.)
Factual error: In any shot of a laptop screen, the operating system shown is Mac OS X 10.4, which was never available on any of the unibody MacBooks shown.
Factual error: There is no consistency in how written language is shown. Sometimes, like the check Bjurman gives to Lisbeth, on Swedish websites, or outdoor signs, they are written in Swedish. Other times, like the documents in the Vanger Corp. Archives, or the Swedish newspapers, and TV news graphics, it's in English. While many middle-aged and young Scandinavians have learned English in school, it is only used in specific circumstances and not for general, everyday use such as TV news or newspapers.