I got both OS, in my iPod Touch and iPhones with my family. I also got the HTC Magic in the MyTouch3G form. I also have Blackberry devices as a third point of reference.
iPhone OS missing a lot of things, and I'm not talking about just the multitasking. The most obvious is a unified message-event timeline which Android, Blackberry and WebOS has. On the iPhone, even if you have push notifications, it can only display one notification on the screen, which is the most recent one. On Android, like on Blackberry, there is a timeline where all the events and messages are gathered, including emails, Facebook notifications, chat messages, and even application updates. Clicking on them brings you directly to the apps in question with the right context set.
Another cool thing Android has. Press on the Home button long enough, and out pops a windows where the six most recent apps opened. You can use this as a task switcher, or go back to apps that are recently opened.
iPhone also lacks real time widgets, which stay on the screen, getting small bits of information that are updated in real time. For example, a Facebook widget. iPhone Facebook app is nice, but it does not have a 24 hour time presence as the Android Facebook app also includes an onscreen real time widget.
Another cool thing about Android, not present in the iPhone OS but to be fair, its also found in the Blackberry OS. The OS is able to extend itself.
Let's say you add a new social networking service. Let's just call it Hofo. If you browse through the picture library on Android, it supports uploading pictures to any installed service. You have not installed Hofo yet, so on the menu, there is no option to share the picture to Hofo.
Now install our Hofo social media app. When you go back to the Gallery, click on the picture and click on Share, you now have the menu option to upload to our hypothetical Hofo service.
On the iPhone you ould have to do it this way.
Go to Hofo app, go to different menus then upload picture from within the app, then post.
On Android, you can do it that way, but also this way.
Go to Picture Gallery, click picture, click Share and pick among the whole list of services [Facebook, Messaging, OurHofoApp, NameofTwitterApp1, NameOfTwitterApp2, NameOfTwitterApp3, Work Email, Gmail, Picassa, Flickr, Babbler, etc,.]
On the iPhone if I go to Photo Albums, click on the picture, and what are my share options? Email, Assign to Contacts, Set as Wallpaper. (The last two options are set on the upper menu on Android Gallery).
Big difference.