Somehow I think it went largely unnoticed that the printable version of the Help that comes with Dynamics CRM 4.0, was published on Microsoft Downloads a couple of weeks ago.  Weighing in at a hefty 499 pages, this guide is specific to the On-Premise version of Dynamics CRM 4.0, but I think you will find few variances in functionality from Dynamics CRM Online.

You can download the guide through the Microsoft Dynamics CRM 4.0 User's Guide.