If you're freaking out about this, don't get your panties in a bunch.
If you think it's the coolest idea ever, don't get too excited.
During an interview with MTV news for the film Miracle at St. Anna (which looks pretty great based on the trailer), actor Derek Luke mentioned Will Smith and Captain America as being connected:
"I heard they offered Will Smith ‘Captain America'"
He added that it "shows how times have changed."
As pointed out in the article over at MTV, Marvel has not shied away from re-casting roles different from type. The original Nick Fury was a grizzly old white guy - a cigar-chomping tough guy. In the Ultimate Universe version of The Avengers (as well as in the cameo in the Iron Man movie) he was re-cast as Samuel L. Jackson, and fans haven't had an issue with it.
This, however, would be one hell of a stretch - and the only reason it might have a snowball's chance of succeeding is because it is Will "everybody on the planet loves me" Smith. I mean if he could make Hancock a huge success this summer, that shows people will show up to see him in a movie no matter what.
He can certainly fit the role physically - he buffed up to big proportions for his performance in Ali, and he's been pretty big and muscular ever since. We've also seen that he is capable of leaving the "Aw, hell no" style behind as he did in I Am Legend.
But Captain America? Just how much are they planning on changing the character and his origin? I mean IF this turns out to be true (which I'm not buying at this point), one thing they had better NOT do is turn Steve Rogers into some snarky, bad attitude guy instead of the well known weakling who wanted to do all he could to help his country.
As far as I'm concerned this sounds to me like B.S. The equivalent of "my sister's best friend's third cousin heard from his next door neighbor" that such and such is true.