I personally believe that football should use video replays for penalty decisions. It's such a big decision that at a guess converts to a goal 90% of the time! In the link Howard Webb admits that he made an error and this totally changed the course of the game and the season!
http://www.news.com.au/heraldsun/story/0,21985,25403139-2883,00.html
I don't believe it would slow the game down because it's either a penalty where the play stops or there is a player rolling around on the ground like they have been shot looking to get a penalty decision. Either way the game stops, the refs are mic'd up so it would be easy to get quick replay, refer the decision to the onfield ref and move on.
Some would argue that this is one of the beauties of our fabulous game and you win some and lose some but many other sports refer to the 3rd umpire and I believe it's time that football does too!
Have to say, I'm still shattered about the way the Aussies were knocked out of the World Cup 3 years ago!!