In my current campaign, I've asked each player to create three PCs. The PCs are merged, so they only play one at a time, but they have to track and manage all three. And to make things worse, they are each using different game systems!
I usually run 2 PCs at once (usu. by cohorts), but sometimes more. And since I am often a necromancer or summoner, I often have to control multiple characters in battle. I try to get everything done in advance to ensure a minimal delay when it is my turn.
Ozmar the Considerate Multitasker