Simple reports of income for a given period of time would be useful for doing taxes later.
Ryan Snyder commented
How about expanding the reporting. If Product were able to be in groups this could really be expanded and really really useful. A user would be able to see how much of a certain product they have actually sold.
I agree with this. I might only use it once or twice a year, but without it, I don't know how I will be able to switch all my invoicing over to siwapp.