I felt the explanation for how Thor returned to Earth was satisfactory.
Now that I'm thinking about it, how much time did pass in Avengers? I've only seen it once, but it seems to me like one, maybe two days.
I wonder how Emily Blunt must be feeling right now. She gave a couple of very high-strung responses as to why she didn't accept the role of Black Widow in IM2 (schedule clashing notwithstanding with the awful Gulliver's Travels). Now with Avengers being a success for the record books whereas her last movie came and went like the Ch'iTauri I am sure she is in the process of firing her agents!
By that token, I wonder if Edward Norton is beating himself up for acting like a diva and getting asked not to return for the film.
Ok, that makes him sound bad, but I know there's more to him not coming back then just salary negotioations.