Via Slashdot, Extremetech (http://www.extremetech.com/extreme/107245-inside-the-worlds-largest-lan-party) brings us a look at the world's largest LAN Party, Dreamhack, held in Jonkoping, Sweden with 12,000 (that's over 9000!) LAN-goers.
Oh, did I mention the 120 GIGAbit (http://www.dreamhack.se/dhw11/2011/11/22/120-gigabit-at-dhw11/) internet!? Even with a pipe that monstrous, I'm pretty sure they had on-site servers (http://www.dreamhack.se/dhw11/2011/11/25/excellent-servers-at-dhw11/) for BF3 and other non-LAN support games.
(http://www.extremetech.com/wp-content/uploads/2011/11/dreamhack-night-shot-640x287.jpg)
P.S. Make sure you check out the slideshow at the Extremetech link...pic 5 specfically ;)