It was actually the 4 step rule (sorry for being pedantic) but goalkeepers could get around it by taking 4 steps, dropping the ball and then picking it up again. This was essentially amended when they changed the backpass rule which banned keepers from picking the ball up again.
Also the 6 seconds only starts once the keeper is standing and is in a realistic position to release it. So
a) if the keeper dives and is on the ground with the ball then the timer doesn't start until they stand up.
b) if they catch it in the air defending a corner then for as long as there are a load of opposition players are around the keeper, the timer doesn't start. Generally a referee will only start the 6 seconds once all the opposition players have left the area.
There is a slight misconception that the moment that the keeper touches the ball with both hands that the 6 seconds starts. This is not correct. In terms of when the guidelines indicate the referee should be starting the timer, you'll probably find that keepers more often then not keeping within the rules.
I think generally referees will err on the side of caution when applying the rule strcitly. If a referee gives the oppositon an indirtect freekick and they score and then someone times it to have been only 5.5 seconds then there will be a lot of scretching about it. I think it is one of those rules that was never supposed to be applied strictly to the clock and is simply a deterent for those really abusing it.
