According to a press release today by the Linux Professional Institute (LPI):
The Linux Professional Institute (LPI), the world’s premier Linux certification organization, announced that in 2012 the organization surpassed two significant milestones: delivering over 350,000 exams and 120,000 certifications worldwide since the organization’s inception.
I suspect that most of these examination attempts were actually the two CompTIA Linux+ Powered by LPI entry level exams (currently LXO-101 and LX0-102), rather than LPIC-2 or LPIC-3.
It would be interesting to see a breakdown of these numbers because they imply a success of about 65% for LKO-101 and LXO-102. This matches my experience as an instructor for this certification for students who have about one years Linux experience prior to attending an exam preparation bootcamp.