I dont think it was a secret at all that Robert Downey would be appearing in the Hulk.
It was to me until I read into this thread. Of course, I don't follow comics, so I have no idea if Ironman & Hulk are friends or whatever.
Same here. I haven't heard it spoiled elsewhere, though haven't been reading up on Hulk much. They obviously have a plan to tie these movies together and I think that's awesome.
PS - I don't think Hulk and Stark are buddies, but Stark and Banner might be science buddies. Or maybe they bring in the world's leading weapons producer to fight the Hulk.