Word is Kenneth Branagh's adap of Marvel's Thor is the secret screening at this years SXSW(South By Southwest Conference And Festival)
South by Southwest (SXSW) is a set of film, interactive and music festivals and conferences that take place every spring (usually in March) in Austin, Texas, United States. They generally focus on up and coming directors and new talent so for a big blockbuster like
Thor to screen there would have to be considered a bit unusual, although SXSW has become one of the world's premier film festivals over the last few years. Apparently there is a screening tonight and then another on Monday.
Chris Hemsworth himself is definitely there, whether more of the cast and director Kenneth Branagh are is unknown for now. Keep an eye out for more news from SXSW as some interviews and maybe even some reactions to the screening are bound to hit at some point.
Update: This appears to have been a rumor started by a spastic over at Pajiba. See Comedian's article above for details.