Well, with instant replays during the match, I'm fine with that. In fact, I'll all for it. I just tend to see that the referees would have a personal issue with it.
What could be interesting is to allow the managers, as they do in American football, the right to challenge (up to twice in a game) a certain call that the referee had wrong.
Another thing to notice is that, if the referees had instant replay, and they decided to use it to review an important event, it might actually break up the dynamics of the game as is, so the players might be miffed about it, too.
All in all, I like instant replay, and I think it would be an important step up in the game's mechanics. In my opinion, in almost every sport that has a referee, the referee can sometimes get a little personal with certain players or teams, and that's the stupid reason why Fergie would get riled, or Wenger sometimes. This is not to say that guys like Mike Riley don't do a damn good job, but the idea of impartiality must and always will be a concern with umpires, referees, and the like. (If anyone knows about the NBA, then you know what I'm talking about.)
"I like refried beans. That's why I want to try fried beans, because maybe they're just as good, and we're just wasting time." - Mitch Hedberg (1968-2005)
"Football is about if you want to run and fight for each other, if you really want to play that killer ball." - Robin van Persie, Arsenal FC