I suppose you can build metrics and decision trees around anything - including when to have party.  TechCrunch just reviewed a site called MyPunchbowl.com

"…MyPunchbowl has made setting a date that much easier through the help of an algorithm that recommends the best date for your party."

Also, depending on who is coming and what level of importance they are (you specify that) the algorithm recalculates the best date for the party and notifies everyone else.

Hmm….sounds interesting.  Here's a YouTube movie that explains the whole thing: