There's an article on InfoWorld's web site about open source CMSes, where five such systems, Plone 3.0 included, are taken for a ride.
Final grades are pretty close, with Plone getting an 8.6, second only to Alfresco's 9.2. Here are the final grades according to the author, Mike Heck:
Alfresco, 9.2
Plone, 8.6
Joomla, 8.4
DotNetNuke, 8.4
Drupal, 8.3
Though Heck seems to be under the impression that Plone uses MySQL out of the box, I think overall he gives Plone a fair review. He applauds Plone's multilanguage support, workflow, navigation, documentation and also most Plone 3.0 new features. Some problems he mentions are the unfinished integration of many ZMI management screens into the plone admin UI, and the necessary use of third party modules for some functionality (he would rather have everything as part of a single package).
It's good to see that Plone and other Open Source CMSes continue to gain a lot of respect.