I did some brief searching and could find any threads even though I thought this was talked about before.
There should be a way to print out a current statement for a customer. For example if they have 2 invoices, 1 is partially paid, I should be able to print out a statement that shows the total from both invoices minus the amount paid and the total they owe.
I looked in reporting and couldn't find anything either although I would figure I would find this on the clients page in the admin section.