Ok, I am getting SERIOUSLY sick of losing my ME when joining a party from arcade and the party I join isn't in a party lobby but has pretty much finished with a map. My suggestion is that there should be a 15 second lock out for any map as soon as a member becomes active on the map. This would prevent a lost of 10 (0r 20 depending on how you look at it) ME from joining parties that have have finished a map. Also, if no parties are in the party lobby then there should be a prompt that lets the player choose to start a party or be alerted when one of the pre-existing parties has started a new map.
Energy is precious. Please let us conserve it and not just drain us of it.
If you go to a gate and choose "Join a Party" then it won't let you join a random party past a certain point in the level.
Clicking on the friends list and select join, however, will always let you join a level no matter where they are in it.