As an additional thought, I didn't really need Contactizer Pro's projects and task management because I already have projects in OmniFocus for various customers. The idea is that if you have a client, you'll usually have a project tied to that one client.

Contactizer Pro would be great for those of you who don't already have a project/task manager.

I usually have to refer to a client in these storage areas

Set up an Apple Mail smart mailbox to catch all correspondences for a particular client.

Create a folder in DevonThink to house all documents such as graphics, invoices, receipts, Word documents, PowerPoint presentations, and Excel documents.

Create a project in OmniFocus to hold all the necessary tasks for that particular client.

Apple Address Book contains basic contact information.

As a GTD rule, try to use as many inboxes as you need and as few inboxes as you need. I wouldn't be able to use Contactizer Pro's projects/tasks features because I already have them in OmniFocus. There was no need for me to duplicate tasks in Contactizer and OmniFocus. Trying to update both would be a mindless waste of time.