| | Couple of shortcuts
Whenever I'm in an app and want to get out and close it, I hit the menu key and press C (for Close) then click the trackball. This will quickly close the app.
Regarding the duplicate emails, I don't do a thing, I'll get duplicates, but when I delete it on my desk PC, it gets removed from my blackberry. If the notification (that you got mail) bugs you, you can set your Profile to phone only or change your active profile to not generate an audio notification when you have new mail.