Francesco Ciriaci has started a series comparing Plone and MOSS in response to a trend of companies choosing between these two platforms. This first article focuses on general features and licensing. Key differences are the obvious Microsoft dependency of MOSS (which could be a good or bad thing depending on your technology strategy), licensing costs, and the availability of modules.
Another usual suspect in a selection for an Intranet collaboration platform with some web publishing capabilities is Alfresco. The Alfresco marketing and engineering department have been beating on Microsoft's door with their Share product. Alfresco also integrates with SharePoint by supporting the SharePoint Protocols.
While there is considerable functional overlap between these solutions, the pricing systems of these products are very different. Alfresco is sold through a per-CPU commercial licensing scheme (customers are advised not to use the free open source Community Edition). Typically this will work out to roughly 40K per year for a medium size company that actively uses the system. MOSS is sold on a per user basis. This is good for small to medium size companies but gets very expensive when MOSS spreads virally across very large companies (as it typically does). Plone is totally GPL licensed and has no recurring support fees (it can be somewhat difficult to find a commercial-style support program for Plone. Email me if you are looking for one. I know some people).