Slider Lock by Ajani InfoTech is a great solution for all of the problems listed above. With this application, you can set your device to auto-lock after a predetermined amount of time, or when the backlight goes off. You can even choose whether you want the app to not lock your device when certain apps are in the foreground. And with the ability to toggle the entire app on/off, and one-click activation, there's no need to worry about your phone doing things you don't want. Once locked, you simply slide your finger across the on screen slider (for touchscreen devices) or use the trackpad/ball for non-touchscreen. Available for most BlackBerry smartphones, you can grab Slider Lock from App World for $1.99.
More information/screenshots and to purchase Slider Lock