Hm… ”Thor” is good fun, so I’m reluctant to release my snark… But who am I kidding? What I’m listing below is actually what makes Hollywood ‘viking movies’ fun to a scandinavian.
*Yes, there are the poetic Edda and the Snorri Sturlasson Edda – Hollywood have looked at all the words in them, and chewed a bit at the covers.
*Authentic viking helmets had no horns, but that’s boring. Come to think of it, helmets with two horns are kinda’ boring too. Let’s have helmets with three horns on them.
*If a helmet has to have only two horns you can spiff it up by make the horns extraordinary looooooooong.
*Asgaardians are not horny  – but they do have a thing for pumpkins.
*Somewhere between the viking age and our time a ship from Star Trek TNG crashed into Asgaard and destroyed the asgaardians’ fashion sense.
*Edna Mode would have a fit as soon as she left Bifrost.
*To make the movie seem more authentic it’s acceptable to toss in one (1) correct viking dress. But only for five seconds on a minor extra. Better encapsule her in ice as soon as possible to make sure the audience doesn’t think the movie is a documentary.
*Odin’s wife (Frigga???) looks very much like a presidential wife of the United States. (I’m quite sure Nancy Reagan wants her hairdo back.)
*Sif’s golden hair  has browned with age.
*If an astrophysicist needs an extra there will be absolutely no unemployed students in the field who apply for the job. Nope. No one. At all.
*There are several good reasons why Heimdal, with the kenning ”the white as”, could have dark skin, but why bother with a hint of those when we can give the character cool, yellow eyes?
*Hollywood has mastered hard words like ”jotunn” and ”Laufey”. (Good Hollywood! Have a cookie!)
*Loki’s mother has undergone a sexchange and some serious plastic surgery 
 The old norse æsir, on the other hand, couldn’t keep their pants on for five minutes. If you read the eddas you’ll find a glorious amount of incidents were gods and godesses ends up in the wrong bed, and an impressive amount of bastards. But don’t read it literally – in many cases these encounters are symbolical.
 Sif, Thor’s wife, had hair made of pure gold. Loki once cut off her ordinary hair and had to replace it magically.
 Heimdall was an important god, who not only guarded Asgaard, but founded the norse society order and did a few other interesting things. He had nine mothers, which is a hint that he is something more than a character in cool stories. My own interpretation is that he stands for the knowledge you gain once you memorized nine important ”books” of knowledge (I’m no expert on norse gods, so anyone more knowledgeable are wellcome to chip in). The kenning ”the white as” is the one most often used for him, but the whiteness is not in his appearance, but in his function. (My favourite kenning for Loki is ”Sif’s hair accident” btw.)
 Laufey was Lokis mother, his father was called Farbaute according to Snorri’s edda. I have no idea why Laufey is picked as the ideal name – is the ice giants hermaphroditic? On the other hand, in religious systems with panteons, sexchanges are not unheard of. Gods and godesses drift over time. When the worship spreads the characteristics of the god changes with the geography, and sometimes a male turns into a female. The chinese boddhisattva Guanyin is a good exemple. In hinduism you can trace these meanderings, a rare luxury when it comes to norse gods. Heimdall was probably more important than we know now, and the god Ull, who is hardly mentioned in the eddas, was probably more important in Sweden than on Iceland where the stories were recorded. Alas – so much knowledge is lost.