A semi-monthly or quarterly meeting where project managers within the organization can share experiences could be an effective option for sharing what's been learned among project managers. Another option might include capturing lessons learned in a wiki that is shared among all the project teams. Different organizations will need to take the best approach for their group.
Don't make learning the next corporate initiative: It's natural for organizations to try to formalize the learning process. "Corporate" is all too often the same as "bureaucratic," which employees are more likely to avoid. Of course, some could argue that making project learning "regular" and "consistent" might require a formal initiative, but if team members sense that the value of a project retrospective is to simply check off one more box for the executive team, it won't be taken seriously.
Don't make learning a one-time activity: Project learning should be ongoing and interactive. Don't let it become an isolated activity that happens rarely.
Some companies rely on project management software to facilitate project learning. Others use homegrown methods. The important things is to create an environment where project learning can take place.
What does your company do to capture best practices and learn from experience?
For more project management tips, see:
Project management: Scrapping a doomed project
Project Management: 4 Questions To Ask Before Starting Any Project
Project management: 4 tips for dealing with problem stakeholders