Hi
Everybody knows Linkedin. Some of the featured groups are really interesting for Project managers, preparing or credentialed already with PMP.
For instance, "PMI credentialed PMP" with 49,538 members:
http://www.linkedin.com/groups?home=&gid=40431&trk=anet_ug_hm
For French Speaking, PMP® - Groupe Francophone, with 3,213 members:
http://www.linkedin.com/groups?home=&gid=1773686&trk=anet_ug_hm
A famous one, with 109,892 members, Project Manager Community - Best Group for Project Management:
http://www.linkedin.com/groups/Project-Manager-Community-Best-Group-35313?home=&gid=35313&trk=anet_ug_hm
The biggest, The Project Manager Network - #1 Group for Project Managers, with 249,251 members:
http://www.linkedin.com/groups/Project-Manager-Network-1-Group-37888?home=&gid=37888&trk=anet_ug_hm