Timer:
If your rotation timer is set to 1 minute or longer, it will not be killed when your device sleeps or when you load an app. This still uses no resources as the timer is in an idle state (blocked is the official term) until the timer period elapses. The reason that this is done is so that longer time durations can be used. If this was not done and you set an hour, then everytime you load an app, that timer is killed. When you close an app the timer is reset to 0 and started again. Your image would never change unless you left your device on springboard for an hour.
With this, you can have longer times. If a timer elapses while locked or in an app, the image will not be changed to prevent any lag from within an app and to prevent all activity while sleeping or locked. But as soon as you unlock the device, the image will rotate.
Random vs Sequential:
I recommend using random display. Sequential display will start at 0 everytime you respring or reboot your device. If you do this often and have a large list of images, you may never see them all and will constantly be restarting at 0.
Winterboard Widgets:
If you have any springboard winterboard widgets such as a stock ticker, clock, etc, they will be covered up by BossPaper. They will still be running and taking up your resources but the BossPaper layer covers them. This not a problem that I can solve easily or a problem that I want to solve.
Grey Icon Labels:
This is the stock color of the iPhone icon labels. Winterboard themes often make them bold or white, but the grey you see is stock, unmodified.
Upcoming Feature Considerations:
Features *NOT* Considered: