I joined Potomac Pedalers last year. My experience was that it depends a lot on the ride leader. Some ride sweep to make sure no one gets lost or dropped, some are more in the middle of the pack. Some leave cue sheets at their cars in case anyone arrives late, others don't so if you're late you're SOL.

The rides I did weren't particularly social. Some rides include lunch either during or after the ride, and I think that's were most of the socializing comes in. During the ride people were more interested in riding than chatting.

I did CC rides and even though I'm pokey-slow on hills I managed not to be the last person to finish. I think the faster rides are the ones where you're more likely to get dropped if you can't keep up.