For bookeeping, we work in Quickbooks using Parallels/XP on a mac because the mac version is crap. That’s for our accounting – but to coordinate between several of us, we keep a full list of projects, payment status, budget codes, etc., in a numbers document on a shared idisk folder. When a project is completed, I update the document, it syncs via mobileme/idisk to the other macs, and then our accounting person picks it up and has all the billable information.
We also use our own pages document/invoice template to invoice clients rather than using quickbooks. We had problems with quickbooks being slow on delivering invoices – I forget what the situation was, but quickbooks didn’t allow a simple pdf export function at the time. Regardless, all invoices are also stored in mobile me servers, so they’re accessible from my iphone or any computer with internet access.
When it’s time to send an invoice, the Pages / Share function is dead simple and provides a rock solid PDF that our clients love. It works, and keeps everybody happy and not completely attached to a single computer.