Re: Downey's last?
If IM3 is Downy's last then they should take a break from IM for a while. I worry that Marvel may run the risk of operating their film division too much like their comic division if they expect to churn out movies from their franchises on a regular basis without fail. The idea of "we have to have an issue out every month" is what ultimately led comics to their doom, because the average reader got sick of being expected to keep up with all the continuity, and the stories themselves felt less and less like an occasion and became so regular that they ultimaely seemed mundane.
Movies have to reach a much bigger audience than the small few million that still read comic books regularly, and that means Marvel is going to have to accept the rules that the film industry has to play by. While comics in their current form operate like a steady flowing stream of never ending continuity, movies have to breath. Right now they are happily inhaling Iron Man, but eventually they're going to have to exhale and breath in something else, or the audience gets bored. Then, a few years later, they'll be ready to breath in Iron Man again, once that's what people want to see again.
I think that's probably why movie franchises tend to come in trilogies-- that's just enough story for people to get a digestible arch. And if you give it a couple years for a break, people start feeling nostalgic about the franchise and you can bring it back for another arch. I don't think that with the way the industry operates though, that there's enough room for every superhero franchise to have the longevity of James Bond. It's an inherently different medium from comics and Marvel would be wise not to expect that they can just keep churning out these movies without ever taking a break.