What's the flakiness quotient these days? How many people whom I invite will show up?

Obviously, the type of occasion and the guest list will affect the numbers. But for bigger parties, when you've invited close friends and distant acquaintances, "a good rule of thumb is to expect 70 to 80 percent to show," says Laurel Szeto, owner of Laurel and Party, a Santa Monica-based event-planning company. Most people who are polite enough to R.S.V.P. are polite enough to show up (or call if they can't). If someone who hasn't R.S.V.P.'d arrives, be gracious and make room.