I've just started using GNU Cash for my personal and business accounting needs and I think it's absolutely fantastic. It's my first exposure to double entry accounting and I love it. However, online marketing/CPA models are a bit different than typical business models where you do work, either an hourly service or provide a tangible product and then invoice. If your costs are fairly low then it's not really a problem, but if you're doing any sort of paid advertising or have scalable costs of any sort such as captchas then you need to keep a tight reign on the numbers. You can use a spreadsheet, but I don't really like that and prefer keeping everything in the accounting software, GNU Cash in this case. So let's take a fairly simple example. 1 CPA account and 1 media buying campaign. We need to keep track of the profit/loss within GNU Cash. The way I was thinking was creating daily invoices to the CPA company(that are obviously just for your records) and then setting up expense accounts for the different campaigns, even setting up sub-expense accounts for the different banners you're trying within those accounts. You'd then set up income accounts for each of your campaigns, with sub income accounts for each banner. This way you can view income statements and cash flow statements where you can see in detail the profitability of your various campaigns/banners as well as various financial charts/graphs. When you get paid for a period you can mark all the invoices as paid and transfer the money from income to your business account. If any of you guys are using GNU Cash I'd love to hear about your experiences with it and how you're using it to help with marketing and in general it would be good to hear about how different people keep on top of the numbers when running large complicated paid campaigns.