Users expect things to work a certain way. For example, pressing the back button on the main menu of an app should actually take you back to the home screen of your device. Unfortunately, a ton of Android game makers ignore this rule and override the back button behaviour to do nothing. Some display an Android textview to exit the app instead. Often, those that don't override the back button indulge your patience by throwing up a "helpful" dialog, "Do you really want to exit? Really? Really really?"... "YES PLEASE!" The worst offenders of this design however, do nothing. That's right, nothing.
Enter "Gears and Guts". This is a great game, but notoriously hard to actually exit unless you press the home button (this doesn't actually exit the app). The main menu screen of the game offers no way of exiting. Plus the back button is overridden to do nothing. Pressing the home button fixes this right? Not really. The app still consumes a significant amount of memory in the background (unless it is auto terminated in low memory situations). Unless I'm missing something, this is quite a shoddy implemetation.
Another annoying appp, widget rather, is the reader for Reddit, called reddit is fun. After reading an article, pressing back prompts the user with the following dialog "Really exit?". Stop nagging me, ma!
So game makers, please follow design guidelines. And for gods sake please don't use Apple's design guidelines on Android. They're two different use cases.