I think it would be really useful to add a 'payment type' drop down to the activity report, so that you can view all purchases and sales in a specific date range by not only if they have been paid, but how.
It would be particularly useful for businesses such as myself who use kashflow alongside there own invoicing system (we do not send our invoices to the customer through kashflow) as many of the current reports available do not include our own invoice numbers, just the kashflow one and this makes reconciliation between both systems a lot more arduous than it needs to be.