The next version of Plone, 4.2 will be released on September 1, 2011. In order to make this date reachable, a freeze of new features will take two months earlier - on June 30th. No more PLone Improvement Proposals (PLIPS) will be accepted for 4.2 unless they have been completed and reviewed by that date - PLIPS recieved July 1 to December 31, 2011 will instead be considered from the 4.3 release - due on March 1, 2012. Future releases will be on the same 6 month timeline.
Calvin Hendryx-Parker, Plone Foundation president, remarked that "I am excited about the Framework Team's initiative to get Plone releases out in such a timely fashion. Setting the community's expectations for releases will help better coordinate resources needed to move the project forward and no one will have to be left guessing when an update will be forthcoming."
The details of the new PLIP process can be found here.
PLIPS are the official method by which new features and modifications to Plone are submitted to the Framework Team for consideration. PLIPS can be submitted at any time, and the framework team will meet every 2 weeks and comment on any new PLIPs that have been submitted or updated. This change facilitates a faster release cycle while also guaranteeing feedback on any changes in less than 2 weeks.
You can find out more about the overall release process by visiting the Release Process page. For more information on submitting a PLIP, see PLIP Instructions.