I found this interesting: The 2008 Open Source CMS Market Share Report, by Ric Shreves. Published by water&stone (www.waterandstone.com, PDF, 5MB).
Summary: WordPress, Joomla, & Drupal have the greatest market share & brand recognition of open source CMS offerings, which if you’ve been following the field would seem obvious. It’s nice to have at least one study that provides some tangible rationale.
Addendum: Multi-site Management with Drupal, Plone and Joomla! is an interesting look at future possibilities with respect to sharing the burden across churches/organizations (e.g. ChUUG).
