As an old school Marvel fan, the tag at the end of the credits made me gasp out loud. I knew that there would be something at the end to tie into the Avengers arc, but I never expected that (the benefits of avoiding spoilers).

As for the Cap trailer. Yeah it looks amazing. I read that they originally planned to have another actor do the pre-serum Steve Rogers scenes (which were much shorter than in the final version), but actor Chris Evans fought with them about it because he believed (rightly) that pre-serum Steve is the heart of the character and it needed to be built up to make Cap believable.