One of the common concerns with Plone has been whether its complexity causes it to perform more slowly than other Content Management Systems. This complexity gives Plone more security, better enterprise controls and ease-of-use for end users, but in the past has lead some to call Plone "heavy".
Jon Stahl, Senior Strategist at Groundwire, has been instrumental in testing Plone 4. His tests show that not only has Plone improved over previous versions, it is now moving past its competitors. His post from January led to some worthwhile discussion in comparing the benefits and drawbacks of the most common CMSs. Matt Hamilton's findings also support this.
As we move toward the official Plone 4 release, we expect that some who had concerns about Plone's speed in the past will be pleased with the progress that has been made. Plone has been able to "lighten up" without losing the functions and features that have helped make it an industry leader.