The Plone (news, site) project has launched a user feedback system for collecting Plone improvement ideas. This tool allows Plone users to suggest, discuss, and vote on ways the open source CMS can be improved.
While the project doesn't promise that every idea will be implemented, they intend to use this system to understand what Plone users want to see added and improved. In particular, the team recommends that anyone interested in contributing to the project should take a look and see what ideas are the most in demand and sound like something they may want to work on.
If you find something and end up working on a significant new feature or change, then you'll pull together a Plone Improvement Proposal, or PLIP. This PLIP will be reviewed by the Framework Team assigned to the major release you're aiming for (as an example, the deadline for Plone 4 PLIPs just passed).
For more information: