I keep hearing about fragmentation but I'm not having that much problems with my app (more than 1 million users). Especially on 4.0+ because manufacturers have

I keep hearing about fragmentation but I'm not having that much problems with my app (more than 1 million users). Especially on 4.0+ because manufacturers have to ship Holo, so you can control the look of your app. What kind of problems devs are seeing with the various 4.0 devices?