taking another break and have been reading around. apparently a lot of you dont understand how the overflow system works and thus are claiming its broke.. its not, it works prefectly and i've been using it to level with my group of 10+ friends all weekend.
here are the things that can cause it to not allow you to join your friend.
1. your friend is on the live server (not overflow). to join someone they must be in a overflow. just have friend log in and out and he will be sent to overflow
2. you must be in the same zone, if you leave the zone, you will likely have to rejoin your friends when you zone back in
3. as you can only have a party of 5 you must first have 1 person join another, then leave group and start inviting other to party so they can join your overflow (this is only if you want to get more then 5 people in a zone)
these are the only things i can think of, but after using the join in feature probably 30+ times this weekend i can assure you IT WORKS AND ITS A HELL OF A LOT BETTER THEN QUEUES.