This is a problem. There is no denying it IMO. I am still the #1 auto forum on my area. Still, I am seeing less registrations and I keep seeing my users gravitating towards FB more and more. The # of users logging in daily is lower. The # of posts per user are lower.
Even GTR Life (IPB) (formerly NAGTROC) Supraforums (VB) and Corvette Forums (VB) are getting less hits. This is FB related.
We may need simpler way for our users to get notified of likes etc on a standalone IPB dedicated phone app. One of the reasons people use FB more is related to their more robust messenger (this is very powerful imo) and proprietary mobile apps.