Guess i'll just toss my 2cents in.
-Camping over a group that was there first i feel is a pretty jerkface thing to do, but its fair game. I've been subjected to that kind of thing, and you do the slow-burn, but you cant draw a line around an area and say "MINE!"
-Claiming a yellow mob is fair game, you should be more upset with whatever you did to lose claim than the folks that cleaned up your mess. It's not stealing by any means, you had your "chance" at the mob, and now he's moved on. Forcing it to go yellow or mpk'ing and all that underhanded stuff is a different story, obviously.
-That 20 bucks lying on the ground is going in my pocket.......that bill went yellow!