I hadn't done anything with other players, so I decided to check out the "Posse Up" option, and got thrown into a random group. Grabbed my headset and hoped for the best, not expecting much.
I must have gotten lucky, because it turned out to be a great group, all friendly and on-mic. We did some story and stranger missions, got into a few shoot-outs, and swapped war stories for a few hours. Made some new Xbox friends, and had an overall great time.
Just posting for those who don't have any friends who regularly play, and who don't expect much from randos. Go ahead and jump in... you never know!