Really good interview with Chris, seems very comfortable, (warning some language!)
http://www.youtube.com/watch?v=0bVpV...feature=relmfu
In the first one he mentions wanting to cameo in Thor 2 but it sounds like it wasn't definite at that time (note he does say that the cameos DO count as a film, for those who have signed for a certain number of films). In the second part (linked on that page) he talks a bit about getting ready for Cap 2.