I often recommend that couples make an announcement in their program and then also during their ceremony for guests to enjoy the event and refrain for photographing it. Three reasons to have an unplugged wedding:
#1 - I've got you covered. Guests have access to all of the photos we take, so they can relax and be present at the event.
#2 - A background full of cameras and not faces doesn't look as good.
#3 - The flash on someone's point and shoot can alter the exposure for our images.
More about the unplugged wedding movement and examples of why this is a good idea with the link below: http://petapixel.com/2013/05/15/guest-photographers-or-why-you-should-have-an-unplugged-wedding/