These groups are very helpful for getting in contact with others who are pursuing the same certifications as yourself. These are informal study groups, where people share ideas, questions, tips, links or experiences. Absolutely nothing that would break NDA!
VCAP-DCD Google+ community for version 510 and 550
VCAP-DCA Google+ community for version 510 and 550
VCP6-DCV Google+ community for exams 2V0-620 and 2V0-621 (I'm the founder, let me know any problems!)
VCAP6-DCV Deploy Google+ community including betas like 3V0-623 (i'm a moderator in this group)
VCAP6-DCV Design Google+ community including betas like 3V0-622
VCIX-NV Google+ community for exam VCXN610 and also lots of VCP-NV content