This can be taken too far. Imagine clicking on a mailto: link in your browser and being taken to email - while you're there, you read a few emails and end up b

This can be taken too far. Imagine clicking on a mailto: link in your browser and being taken to email - while you're there, you read a few emails and end up back at your inbox. You're done, and you're "at the top" of the app. You want to get back to your browser. How do you do that? I've seen an email app that, under these conditions, pressing back makes you go through every single email you already read. In other words, it traces you back through every single Inbox-->Email-->Inbox loop you ever did. Not to mention what happens in the same app when you muck around the settings screen. Be prepared to go visit the settings screen again! The problem here was that there are two ways to go "back" when reading an email. Press the back button, or clicking an on-screen UI element that took me back to the Inbox. One of them pops an item off the undo stack, and the other pushes one onto it. It's consistent, but frustratingly so. I realize that I want to have my cake and eat it too, but at some point having an undo stack that is 30+ items deep doesn't really help me all that much. I suppose it just goes to show that the meaning of Android's back button is way too overloaded (I think WP7 suffers from this across their other buttons as well).