Haha, most of the TV ads I've seen haven't been too bad on spoilers. There's been a few new things shown, but nothing too bad assuming you've seen the full lenght trailers. I heard the Widow clip kinda mentions a spoiler though.
IGN's actually doing a pretty cool set of inteviews with Whedon and some of the cast, like RDJ and Chris Evans. I would post a link, but the forum doesn't seem to want me posting links right now, for some reason.
I read a good amount of interviews that Collider had with the cast and Whedon and Kevin Feige. They were pretty cool. A lot of the cast joked around a lot and they really seemed like they were having a good time making the movie.
Yeah, all the interviews I've seen are real encouraging about the movie. Whedon, especially, really seems to be excited about making the movie, and he seems to get how to make a movie like this and to know what fans want in an Avengers movie.