From what we've been told all along about the Thor movie, it would entirely take place in the mystical Asgardian realm, with only a tiny part of the movie (likely at the end of the film) taking place on Earth.
Strangely enough however, Variety's article on Tuesday about a recent cast addition (more on that below) contained a sentence reporting that the story of the Thor movie "centers on a partly disabled med student who discovers his Norse god alter ego, the hammer-swinging Thor."
For those unfamiliar with the comics, this med student goes by the name of Donald Blake who's Thor's other identity. Why or how? Well, Thor's farther Odin wanted to have his son, the God of Thunder, to learn humility and thereby puts Thor into the body of Donald Blake as an act of punishment for his reckless behavior. Odin places Thor in the body of Blake who suffers from a lame leg and Thor acquires his memories while losing his own of being a god prior to this event.
Later, Blake finds the mighty hammer Mjolnir (hidden in the form of a cane) and gains the ability to switch between his human form or that of The Mighty Thor. Without a doubt, this will - in one form or another - likely be the link to how Thor becomes an Earthly being, leading to his interaction and eventual membership with the other members of The Avengers in the upcoming Marvel Studios' films.
Getting back to Variety's report - the focus of the article is for another talented cast member joining Branagh's mighty roster: Kat Dennings (Nick and Norah's Infinite Playlist, Charlie Bartlett) has officially joined the cast of Thor and will play the character of Darcy, who works alongside Jane Foster (Natalie Portman).
So, Variety's statement about the story doesn't seem to be the case from what we know so far and the story may not center on Blake at all, but may only include him during part of the movie - we have to wait and see on how that part of the story unfolds.
So while it may be obvious that Donald Blake will be included, or at least introduced, in the Thor movie - especially with the fact that Natalie Portman is playing a nurse of Blake's and his love interest - It may not be the case. Hercules at Ain't It Cool News may have found otherwise. From Hercules's post:
"Variety’s assertion contradicted some of what we’ve heard, so we contacted a 100% tested and solid source, someone intimately familiar with the movie Kenneth Branagh is making, and he or she tells AICN Donald Blake is definitely NOT in the movie."
That's strange. Does that mean when Thor reaches or enters our realm, he is only Thor? Then what are Natalie Portman and Kat Dennings' roles for and how will they interact with the title character? I'm not sure I buy that Blake isn't in the movie at all but if he isn't, I'm curious in how the character will be handled when he's banished to Earth and meets our human characters.