http://en.wikipedia.org/wiki/DreamHackQUOTE
Dreamhack Winter 2006 was officially announced by Guinness World Records to be the world's largest LAN party. As of October 15, 2006, ten thousand tickets had been prebooked according to the ticket system. At 18:33 local time on the first of December, a representative from Guinness appeared on stage to announce 7,752 attendants present and 7,788 computers connected to the network. As the summary was made after the party, the world record was set at 8,531 unique computers and 9,184 participants [2] during DHW'06. With temporary visitors, sponsors and crew included, the total attendance of DHW'06 was 10,638 people according to DreamHack AB.
Edit: ohhhh longest lan

meh!