I myself was just wondering if there was a way to "mass bill" all SO that are in the state of "Pending Billing" when I got in here, but that's not the same as what JayB was asking. Maybe mine's simpler?

Transactions - Sales - Invoice Sales Orders

or a map/reduce script as someone else mentioned

in our case we're not really using invoices. Most of our SO are paid through cash sales. Basically we hit the "Bill" button, it loads a cash sale form, and we hit "Save" right away, and it does its thing. However we have to do that process on all SO individually.

The Invoice Sales Order batch process will create Cash Sales when appropriate (credit card associated to SO or Cash payment). If there is a customer deposit against the sales order, then an invoice will be generated and the deposit will be automatically applied leaving the invoice in the fully paid status.