Awesome. According to this PetFoodAlpha post, a Final Fantasy XI guild went up against one of the big bosses in the MMO last week and had to quit after fighting constantly for 18 hours.
The baddie, Pandemonium Warden, apparently changed form 20 times during the battle, which left players literally passing out and vomiting with exhaustion.
Lightweights, clearly. More through the link. Thanks, Kotaku.