I've never used an Android phone, but surely that's a little confusing for casual users – at a glance is it easy to tell which is the "main" screen?
One screen to the right are the rest of my social media things and various camera apps plus the powerbar widget for turning on and off various things on my phone without heading into settings (flashlight, wifi, GPS, etc.)
One more screen to the right are my various nerd tools, an ftp server, a terminal emulator, file manager, heck I even have a tricorder app and the tron bit on there.
Going left I have productivity apps, google docs, drop box, a folder full of various audio apps like pandora and Tune In radio, The Kindle app, a comic book reader, etc.
And finally all the way left I have games, emulators, calculators whatever sort of entertainment junk I want.
I know immediately where I am on my phone at a glance and can almost navigate to it without looking.
If I start to run out of space, or want more organization, I just dump a category of apps into a folder...or my Launcher lets me add more screens if I want.
The "back" button goes back to the last thing you were looking at (a sort of stack based approach kinda like a web browser, but across the entire OS).
So if you are in an app, launched from the left-most screen, and want to get to another app on the left-most screen, you might hit "back" and it'll background the app and put you on the left most screen.
Given the same scenario, if you want to go to the right-most screen, it's easier to just hit "home" and swipe twice.