My group has played 3.5 for quite a bit, and now we are with pathfinder. One of us likes to play rogue,and is used to work in tandem with our wizard to take advantage of grease in order to land some free sneak attacks, and was disappointed that he could not do the same in pathfinder without some other person helping them to move his target to trigger an attack of opportunity.
So he try the following tactic: he ready an action to move adjacent to a enemy in a greased area when he start to move in order to trigger an attack of opportunity due movement. I do not see any problem with that and allow it.
Later, the player reads that you may take a 5 foot step as part of you readied action, and proposes an new tactic: Since he acts after his target, he moves and remain at 5ft of the enemy in the grease area, and ready a 5ft step + attack with the same trigger. When the enemy moves at the next turn, he eats two attacks, the readied attack and the attack of opportunity (as described here). The attack of opportunity is a sneak attack, as before, but the player says that the readied attack is also a sneak attack, since it landed while the enemy was moving, and thus flat-footed due grease effect.
By the rules, a readied action interrupts the action when it is taken, but I'm not entirely sure if in this particular case the enemy has already started moving (and is flat-footed), or he takes the attack before moving, (so he is not flat-footed) and then moves.
At the end, I ruled that the readied attack took the enemy flat-footed and was a sneak attack, both because I like my players using tactics, and because the drawbacks and the work needed to set-up the maneuver were a more than adequate cost for the advantage gained, and I'm fine with that as a house rule, but now I'm curious: There is any rule that explicitly back-up (or refutes) my decision?