9. Disorganization to the max.
I once attended a wedding where the cocktail hour became two-and-a-half hours long because the bride and groom wanted more photos in the moonlight. Imagine the look on guests' faces when we finally sat down to our seats and waited another hour and a half before dinner was served.
How to deal: If you're unable to hold the ceremony and reception within two hours of each other (guilty as charged), make other accomodations for your guests. For example, my reception site has a waiting area where drinks and light refreshments will be served for early birds. If your reception/ceremony space is sprawled out, consider using sign posts to direct guests to necessary landmarks, like the dance floor and bathroom.
"Just how long are you going to make us wait?"
Photo Credit: Ashfall Mixed Media, Inc.