I haven't tested it or anything specific, however, I have noticed that paths seem to get messed up before going some place.
An example: A couple leaves the house heading downtown, they both get in the cab and head for the subway. When they get out at the subway, the group leader takes off running downtown, from the suburbs, while the follower takes the sub downtown and has to wait while the leader runs all the way.
I have tried to cancel the runner(leader) and send him again but then I have to keep the follower at the destination or they tend to wander away.
If I know I am going to group up, I will invite people to the location, then group up and then things go pretty smoothly from that point.
Of course this example is only in bridgeport, I have not gone back to one of the other cities until I decide on like/dislike of bp yet.