This rule has been scrapped from International cricket now. It was supposed to be experimented till the end of 2005 but was scarapped at the end of April 2005 only when all International captain protested against it. The real reason for ending this following Super Sup rule was that it was very confusing for the captains and rarely made a difference in making tactics for an ODI match.
The time ICC made the changes in ODI cricket and converted first 15 over Field restrictions into Power Plays, they also introduced a completely new aspect of substitutes in ODI cricket, called as Super Sub. As you can see in the picture of the Lords cricket score board, Vikram Solanki was the first ever cricket player to be a super sub, substituted in place of Simon Jones of England.
Previously, when captains went out on the cricket pitch to do the toss, they exchanged their final eleven. Now, they exchange 12 player names, with 11 in the starting eleven and one as the super sub. The super sub can come into the game anytime of the match in place of any other player, either after the first ball or only for the last ball, but the moment he comes, one player has to go out and he can't come back and take any further part in the one day match any more.
The super sub can do anything the captain wishes him to - bat , bowl, field or even keep the wickets. Previously, the substitute fielder was not allowed to bat of ball or keep the wickets. He was just allowed to field in place of someone, but now Super Sub can. Don't confuse, this rule is not applied in Test match cricket!!
The International captains has asked ICC to change the rule a little and allow them to name the super sub after the toss, so that they can analyze and then decide which player is better suited to be the Super Sub. For example, if a team bats first, and feels that the pitch is good for batting, he can chose for a bowler as his super sub so that he can be super subbed with one batsmen when the fielding time comes. Right now, its more of a guess about whom to take as super sub.
Know about Power Plays in one day cricket.