It should definitely be introduced, if only for goal line incidents. It would prevent terrible injustices like the England "goal that never was" against Germany. Being English I may be biased when I say that if that goal had been allowed and England had got their 2nd goal within a short period of time, then the result COULD have been alot different, but thanks to FIFA, we will never know.
I support Bolton Wanderers in the Premier League and my team were relegated in the 1997-98 season on goal difference. Everton were the team that stayed up and during that season, in a game against Everton that finished 0-0 Bolton had header which bounced well beyond the goal line, but the referee claimed it was not a goal. This one mistake left Bolton 2 points worse off and caused us to be relegated, only returning to the top flight 4 years later and in a much worse financial situation.
If goal line technology can prevent injustices like this occuring, and will not slow down the game too much, then they should be introduced. It works fine in Rugby and Cricket and noone complains about that.
Football needs to move with the times and take advantage of the technology that is available today imo