I'm a member of the Del Val chapter. I've been for years. I'm even a Hike Leader. Problem is that with my time constraints, I have a hard time getting out on the trips, and when I do, I balk at the time commitment necessary to do their trips (too drawn out).
I usually look at the activity listings and circle a few at a time for my calendar, and see what my schedule looks like during the week heading into it, and if I'm free, I'll contact the leader (Yes, other family and social plans take precedence over AMC group hikes). This rarely comes together for me. Most of the time, I refer to the trip listings for solo trip ideas for myself at a later time.
When I get free time to go, I usually don't know my availability and destination until a few days before the outing, so joining an AMC trip is usually out (trip filled), and leading a trip is out too because of the listing deadlines for the trips (Tuesdays).
While it would be nice to be a bit social when I hike, I tend to shy away from the over-social aspect of the AMC hikes. The paces tend to be a bit unbearably slow (<2mph), and the meeting times are a bit late (10am?). With my narrow windows for outdoor activities and desired pace, sometimes the AMC trips don't cut it for me. I don't want to allocate 6 hours of my Saturday for an 8-mile hike (with possible group meal afterwards :p ). If I want to get out for 8 miles on my own, I give myself 3.5 hours (plus driving), and get done with it early.
I have yet to find a good group of hikers/BPers with similar abilities, interests, and time constraints. I've made friends with a few members, but it remains that - a few.
Despite all this, there is one recurring trip that I absolutely make time for - the Pinnacle Full Moon hikes (PM me for more info). Located about 40 minutes from me, I thoroughly enjoy getting out with my friend (and trip leader) to see the full moon rise over the PA farmlands.