For one EVE online player DBRD (aka the "boat") it cost him a lot. A simple miss click in a drop down menu jumped his Titan (biggest ship in the game) into a hostile fleet instead of his own. A rescue attempt was made to save it bringing the whole coalition's capital fleet. However as everyone he had pissed off in the last year came to kill him. The rescue mission went south fast. In the end it cost his coalition ~840 billion in game credits. That is a lot of in game money. There was at one point in time ~2800 players in that one system fighting each other. Which at the time was about 10% of the people online playing the game.

Full in-depth battler report below.
http://themittani.com/news/asakai-aftermath-all-over-cobalt-moon


Video of the fight: (all those red flashes are capital ships jumping into the fight)
http://www.youtube.com/watch?v=TLqb-m1ZZUA

Funny thing is I logged out 10 minutes before this all went down. This fight happened about 24 hours ago too.