As of the last major patch, party position is in the order you invited the toons to the party.

Party1 refers to the leader if you're not the leader, but it refers to the 2nd toon if you are.

To use a party based system, you need every toon to promote the new active toon to party leader, whenever a switch takes place. This is the same as every toon setting the active toon to their focus target, should you use the focus based system.

The focus system costs you the use of your Focus for disguised burst or remembering crowd control.

The leader system costs you a second action bar. This is because on every toon other then the leader, party1 will refer to the party leader, ie its the same as pressing F2. If you lead the group and press F2, then you get the second target.

So when a toon becomes the leader they need to page to a second action bar. This second bar has similar macro's to the first, but none of them assist. We don't want the leader to assist one of the followers. Each leader also needs to page back to the first action bar whenever they stop being the leader.

A party leader system will not work in battlegrounds, because you cannot control your placement in groups, and as of 3.1, you cannot be moved from a group to another group, unless the battleground leader is from your server. Which means, they cannot move a toon from another server out of your group. Anyway, if you don't pvp in battlegrounds its much better then a focus system.

You'll need one switch macro per toon on the team.
The same as one focus macro per toon on the team.

When a toon is becoming leader, the macro they press will differ slightly.

If you're not the new leader, you'll press something like this:

/promote NewLeaderName
/changeactionbar 1

If you are the new leader, your own macro will look like this:

/jamba setmeasmaster all
/changeactionbar 2

So when you're not the leader, you attempt to promote the new toon to being the leader and you switch to the first action bar, where all your spells will read like this:

#show
/cast [target=party1target] Lightning Bolt

When you are the party leader, you tell Jamba to make you the master for addon purposes. You also page to action bar 2, where you've just dragged Lightning Bolt from the spell book and don't even have a macro. There's no need for a macro, when you're casting at your own target.