I could be wrong here but dont the rules state that all attacking players should be behind the play the ball. I was under the impression it was but I have never seen it pulled up

It does, any attacker in front of the play the ball is offside until they retreat back behind the point where the ball was played.
Brent Webb was pulled up for it a couple of years ago, and IIRC a Cas player was pulled up for it against Wakey last year? Not sure of the particulars but have seen it pulled when the offside players get involved in play.

IIRC if you are offside when the ball is played you cannot be involved untill the next play the ball assuming you manage to get back onside, that is why Webb was pulled up he waited for the play to pass him and recieved the ball correctly but was still classed as offside.

<pedant mode> You are "out of play" unless you then get involved in play, it is only then you become offside</pedant mode>

Like has been said above, if you're infront of the play-the-ball then you're counted as offside until the next play-the-ball.

It has been pulled up before. I remember Kirk Yeaman having a try disallowed either last season or the season before because he was infront of the play-the-ball.
The try went up to the video ref and was disallowed.