I don't use auto team, ever. I have not had a single good experience with auto teaming. it is worse than a PUG. For some people this is a good feature and I hope they enjoy it. I just have not been all that lucky with it and don't want to deal with awful groups.
Personally I like to do things in my own time at my own pace. That way I don't bother anyone else if I'm going too slow or too fast.
Personally I think the auto-join is a good concept for single instances at a group level difficulty. However, where it falls down is that when you exit that instance, you are still joined with that team. Which is not a good idea for those who then want to do their own thing in an instance that is geared for soloing and not to the group size. Of course, they could just then leave team, but it could be a little bit more intuitive in my opinion.
My suggestion would be a slight modication to the system:
If you joined a team via the "auto-join" feature, then it should also allow you to "auto leave" the group when the instance is completed and you exit the instance, much like leaving a cross-server group in wow auto removes you from the instance. I suggest this because of the nature of the instances when they gear the npcs in accordance with the group size and level.
Of course, if you joined a team due to a personal invite, then you shouldn't be automatically removed when you completely and exit the instance.
AFk'ers and xp-leechers are another issue. If it isn't implemented already, then when a group is auto-formed the system should appoint someone as a team leader so that person can kick a player if desired. To also combat such individuals, xp and loot rights should only be granted to those group members who have "tagged" the npc (i.e. damaged it beyond a certain amount e.g. 10%)
Personally, I see the auto-join feature being espeically useful in the public large battles, like the Deep Space Encounters and Fleet Actions. In those, you aren't being hampered whilst others read mission text, and nor are you being dragged through the instance as quickly as possible, faster than you'd like.
I have auto-teaming on and it's put me on a team maybe three times. I don't have a lot of experience with teams because of that, but based on what I have experienced there are some issues with it.
1. On away missions the person who gets to the NPC first gets to read the dialog. The rest of use are screwed. For example we beamed down to investigate the needs of some miners. I talked to some and the other guy talked to some. I had no idea what the NPC's he talked to said. I had no idea what the conclusion of the mission was because I didn't get to complete the mission, the other guy did. To top it off, the mission didn't complete because I wasn't able to talk to all of the people so I had to do the damn thing a second time by myself!
What good is teaming if we can't take part in the entire mission? What good is teaming if we have to complete the missions solo to get credit? Seriously.
2. I entered an instance and was joined to a team for a space mission. The other players were nowhere to be found. The game said we were all in the same instance, but I couldn't find them and they couldn't find me. I ended up just leaving the group and doing the mission by myself.