With the long lines at some attractions, what is the etiquette for holding someone's place in line? Say that I make a run to Buzz Lightyear to get a Fastpass while my wife and two kids are waiting for Space Mountain. Can I rush back and get in line with them, or is that a no-no? What if I have to take my DS to the bathroom, can the other two hold our spots?
For example: I'm talking a 50 minute wait for Big Thunder Mtn. and a family of 8 shows up just before we go down the final ramp as one person held their spot because the rest of the party was already on the ride using fastpasses and now they want to go on it again! Same thing on Peter Pan. We entered the line during the fireworks, and after the fireworks all these people jump into the line b/c one person "held" their place. I just can't believe how rude people can be! This seems to be getting worse every trip we take. I guess I can understand if there is a child who really has to go to the bathroom and a parent needs to take them...in fact, I believe the CM at the beginning of the line gives you something (card or something) to go ahead and do that. 
Completely rude, in my opinion.
Can you imagine being in line and getting shoved back to the end when a herd of people just show up filing in front of you with their groups?

I always used to overlook it but I've become SO sick of it that I will say something now to the offender, or move their stuff. 
You are the guru of all Disney knowledge and you impart said knowledge without any sentiment or drama...just the facts. You ROCK!