My #1 pet peeve about wedding is NOT knowing who everyone is at the wedding. For my wedding, my wife and I created a small book with photos of every single person that was going to be at the wedding, and a little blurb about each person
we made a copy for everyone, and handed them out the evening before the wedding. People could flip through the book and quickly know how everyone is associated with the happy couple.

I told my friends about this genius idea, and created them a prototype book for their wedding. It was a total humorous joke, but got the point across. They ended up using my idea and creating an amazing book, handed it out the evening before their wedding and everyone knew who everyone was at the wedding. Awesome.