When SharePoint was first released I recall having a conversation with a fellow colleague about the possibility of customising SharePoint as a CRM application.
A company called "BPA" did exactly just that, and named the product "Easy CRM SharePoint" (Easy CRM software solution for Microsoft SharePoint). They have flash demonstrations for this CRM application, and it proves to be very interesting indeed! Click on this link to see it: http://software.crm-sharepoint.com/default.aspx.
So how did they do it? Does it integrate core CRM functionality into Outlook? Would it be better than Microsoft CRM 3.0 itself? Well, having a bit of a look into it, it appears they've used a series of lists, calendars and custom web parts to contribute to CRM functionality. They've even got lists of reports, offline access, an Outlook connector (to attach emails to items) and more. However, as compared to Microsoft CRM 3.0, it does seem like a little child, but I'll leave that to you to judge.