I love the sidebar, keeping it hidden and alerting me to sales from my eBay store. It's a great tool that helps me to ship faster.
One suggestion I have would be to allow the user to change the different sounds associated with events. For instance, no matter how often I hear the 'sold item' sound, it still makes me think there was some sort of Windows error. It would be nice to be able to change that to whatever .wav file that I'd like. The sound of a cash register opening would be great.
If you don't list it, they can't buy it.