Just because Cousin Lenny learned PowerPoint doesn't mean that wedding guests need to be subjected to a tender montage of the happy couple's courtship. The reception isn't a business meeting; it's a time to eat, drink and party!
It's not a total faux pas to project pictures of the bride and groom somewhere discreet and unobtrusive, but the guests don't need to see another show after they've made it through the ceremony itself. Everyone has earned their chicken and white wine. Don't ask them to sit through a seemingly endless stream of pictures of people they've already been staring at for an hour while making them listen to acoustic Green Day covers.