Sorry, I bought Galaxy Nexus instead of iPhone 4S. But, I have tested iPhone 4S every time I had chance to hold. What I had liked about iPhone 4 and 4S was its superiority on smoothness until Jelly Bean came along. I have 3 launchers with my Nexus, one of which is 'Fake iPhone Launcher' which supports iPhone icons and same UI. Now, I could compare mine with iPhone 4S. Result? iPhone 4s is not superior anymore in terms with smoothness. Maybe with the increased...
I am sure Apple would gradually support true multi tasking with their improved specs for future products. http://www.businessinsider.com/ios-6-multitasking-2012-9 Sorry I dont know anything about API, but my Galaxy Nexus is much smoother than iPhone 4S. Why you should not expect that?
I have Galaxy Nexus with Invisible Shield Maximum Protection. You know that Galaxy Nexus has plastic back cover, but the film went well with it. I think it would be ok to the metal back. See the installation guide on the web and take your time when you apply it. Agree with you, I also hoped iPhone 5 with aluminum back in November last year before I bought my Nexus.
If you look at the first image in this article, you see that it does not have protective edges covering front glass edges. And I like iPhone 4 design better because it is awkwardly long and would not provide better reading if you hold it vertically. I don't like two tone design at the back, I would rather have glass back with Invisible Shield on the back of course. I like, though, the thinness.