We were there last week, and I have to say I saw very little egregious line-cutting. What little I saw was 1 person catching up to his/her family, or a parent and a child moving up to meet the other parent and child(ren). And nobody had a big problem with that.
What did crawl all over me (pun intended) was the # of times groups would walk into an auditorium and plop down right in the middle of the row. That happened every single time, and as the CM in Philharmagic pointed out, it's a safety hazard because crowds were large and everybody had to crawl over them to get a seat.
I'm with you--I don't have much of a problem with families that keep one placeholder in line. I would much rather benefit from the hopefully better behavior of rested children than make everyone stand in line with their little ones for "fairness."
I'm also with you on the people who sit in the middle of theatres. I won't tolerate it. The last time this happened, we just stopped the line right there and explained firmly with a smile that they had to keep moving, it was the rules. When they resisted, I said, "It's Disney World, folks. Let's all use our best manners." If people are going to act like kids, I'm going to talk to them that way! As more and more people were staring at them expectantly, and the repeating announcement got back round to the part that said "everyone please go all the way to the end of the row", they eventually reconsidered their bad behavior and moved along. It was a little awkward to sit next to them after that, but everyone around us had a smile of approval when they moved.

LOL
What a wonderful idea!
We decided we better take the kids somewhere since we are leaving them at home when we go to WDW in three weeks...adult only anniversary trip, baby!!!
Unlike WDW I did not notice one line cutter and, trust me, it was OVER crowded...their logic must work, just wish WDW would take note.