Seth Gottlieb and friends at Optaros have followed up their well-received white paper on open-source web content management systems with another run-down of open-source document management systems.  Both papers presented quite favorable reviews of Plone.  And, if memory serves, Plone was the only product Optaros reviewed in both papers.

Optaros' point of view is decidely large-enterprise-centric, but they present a solid overview of the product landscape, and smart analysis of the strengths and weaknesses of the tools.

Plone's strengths were:

• Usability
• The "large and prolific" Plone community ;-)
  
• Strong workflow
• Accessibility for disabled users
• Documentation
• Many ways to access documents (WebDAV, FTP, Windows Explorer integration, External Editor)
  

Weaknesses:

• Lack of strong, built-in versioning (although CMFEditions was noted as a strong emerging add-on product)
• The relatively opaque nature of the ZODB