Check out this Geocaching.com blog article on Lab Caches. I had the opportunity to find 6 of them recently while in Las Vegas. They had been placed for the Geocoinfest Mega Event. In short, they are temporary caches placed for an event. Groundspeak is just looking for a way for event attendees to log the temporaries without multiple logging of a permanent cache identified by the event organizer to be used for that purpose. Right now, they are in experimental phase and are just being tested at mega events. Although they show up in your Find count total, they don't figure into your statistics, which is something I don't like about them.
"Wildness is a necessity." -- John Muir
"When you go to hide a geocache, think of the reason you are bringing people to that spot. If the only reason is for the geocache, then find a better spot." – briansnat