In what way would a no offside rule improve the game? I couldn't see teams effectively attacking as a unit. It would probably mean that the midfield would become clogged with one team trying to cancel out the other.

Agbonlahor was actually heading away from goal when Vidic tackled and was therefore not denied a goal scoring opportunity. Phil Dowd made the right call. Its a technicality but according to the rules its the right call. FIFA are looking into this rule right now because of the triple whammy effect on the offending team. The opposition are awarded a penalty, the offending player is sent off and receives a suspension ruling him out for up to three games. This rule is unprecedented in the game.