I saw it on Youtube, in low quality. There really weren't any spoilers in it, except what anyone can figure out has to happen with Cap. It's a teaser, and it does just what a teaser is supposed to: Give you a slight taste of what's to come, while giving practically nothing away. They're all coming together in 2012, and that's about all the information that's conveyed. Personally, I suspect Whedon's gonna hit it out of the park. If anyone can pull off a superhero ensemble movie, it's that guy. Possibly the biggest Marvel fanboy in Hollywood, and a writer who has proven himself quite capable of writing an ensemble cast of flawed heroes in a way that doesn't feel unbalanced, as well as a skilled director.
However, his style doesn't always speak to everyone, and there's definitely a risk of that seeping into The Avengers, resulting in some people finding it in some way cheesy or confused, which would be understandable, but I for one am very much looking forward to seeing how it turns out.