The next World Wide Flash Mob (WWFM VI) event is scheduled for next Saturday, 11/14/09. "What's a Flash Mob", you say? Well, in the geocaching world, the World Wide Flash Mob Events occur all around the world, coordinated so they happen all at the same time; Oh yeah, and, they are only 15 minutes long! Everyone appears at the exact same moment (10:00 AM PST), signs the log sheet, partakes in some specific act of silliness determined by the event organizer. Then everyone disperses at exactly 10:15.
As of this posting, there were over 100 WWFM VI events planned world wide. This link simply displays the results of a standard geocaching.com search for keyword = "WWFM VI". Unfortunately, this listing won't help you find a flash mob event in your area, as it seems to be sorted somewhat randomly; or not at all. Luckily, a geocacher named Novac has gone to the trouble of creating a bookmark of all the events, sorted by country, then state/province.
If you can find a WWFM VI event near you, I highly recommend attending.