In an interview conducted with Marvel's Kevin Feige, questions about the coming Captain America movie were asked and answered, further defining what we will be getting... and what we will NOT be getting--namely Matthew McConaughey
Feige was asked if the Captain America film would be a period piece. He confirmed yes, the story will take place during World War II, just like the comic book origin story. He says they plan to remain very faithful to the source material and completely traditional.
Feige also confirmed that it was definitely the Captain America shield that was seen in IRON MAN on Tony Stark's work-station as he's removing his suit for the first time. It's just an Easter Egg and probably won't have anything to do with the Capt. America story.
What about that casting rumor making its way around the web that Matthew McConaughey would be taking on the role? Nope, Feige says that's absolutely false.