I think it's been mostly said here, but I did have something pop up on Strava that I thought was a little odd. I ran a workout on the local track and there were a few people doing the same. It just so happened that my workout and another guys workout lined up pretty close to the point where we were occasionally running fairly close together. I had no idea who this guy was, like I said, it was all just coincidence that we ran for at least a few minutes together.
I posted my workout and it AUTOMATICALLY put this guy into my workout as part of my "group". Now for me that's no big deal, we both commented on each other's workout and moved on. Totally normal and nice guy. But I could see how someone could easily run with or near someone just to have Strava automatically connect them with that person.
This might just be another privacy function people will want to turn off that is automatically on.