Some people I know have switched because they got bored with iPhones, saw that in many cases it doesn't "just work".
If you look at the crash logs you'll find that iOS apps and functions crash a heck of a lot. iOS just doesn't tell you something has crashed. Android of course will tell you that the app has stopped working.
Performing simple tasks on iOS can be a chore compared to Android with needless extra steps. Want a ringtone on your iPhone? You either have to buy it and hope it's the right 30 seconds you wanted, or go to your Computer, trim down the song, convert it to .m4r and then drag it into iTunes and sync. Android? Drop an audio file into your "Ringtones" folder. On iOS the apps often have no consistency, sometimes the back button is on the bottom, sometimes it's on the top, same for the other buttons.
On Android the back button is always on the bottom right where you need it, no matter what app you're in. iOS apps are often gimped in their features compared to the Android versions, on Dropbox you can can only upload Pictures and Videos in the app, on Android you can upload any file you want. When I had my iPhone I wanted to make edits to a .txt file in my Dropbox, it wouldn't let me. When I got my Android phone it let me do it no problem, (This was months ago when the iPhone 5 launched so let me know if this has changed in an update).
In another app If I get an option to upload a picture, I can upload from any service on Android, iPhone? You can only take a new photo or use one from the Camera Roll.
Don't get me wrong I've used every iPhone except the 3GS and loved them all, but when Android finally matured enough to interest me (Jellybean update) I gave it a chance by buying a Nexus 7 and loved it so much I bought a Nexus 4)