Play Offense - We can't prevent emergencies from coming up, but we can do our part to make sure there are no mix-ups over the time or misunderstandings about expectations. If it's important that all the guests arrive at a certain time, make sure that they know. We also like to send out a friendly reminder the day or two before our party with details on time and place.
Have a Long Cocktail Hour - Whether we've invited two guests or ten, we like to give ourselves a bit of a cushion between when our guests have been invited to arrive and when we actually plan on serving dinner. This gives us some pre-planned wiggle room if someone is running late (or if we're behind on cooking!).
Keep a Plate Warm - If one or two guests are running really late, we think it's fine to go ahead and get the dinner started. We make them a special plate, cover it with aluminum foil, and keep it warm in the oven until they arrive. This way, other guests can feel free to help themselves and the late guests feel cared for when they arrive.
What other ways do you deal with a late guest?