According to PCGamesN, Far Cry 3 will not have dedicated server support for the multiplayer on PC. Ubisoft has said that if you want to play Far Cry 3 online, you'll have to play as Atlas and host the server yourself. “The online experience does not support dedicated servers” said the Ubisoft community manager MSV-Vextor on their official forums.
Far Cry 2, at launch had also not launched with dedicated servers, but it was added unofficially by server providers, who found a work around to do so.
Dedicated servers, for the people who do not know what it is, is a multiplayer game server hosted on computer servers which have high bandwidth and fast CPUs so that the online experience isn't hampered, which can happen if a particular person is hosting a game and has low bandwidth and/or a bad CPU.
Below is a trailer which shows off the realistic virtual world.
http://www.youtube.com/watch?feature=player_detailpage&v=pF-Hxw-CcMs
Far Cry 3 is supposed to launch in the last week on November, and is looking to be very promising. The single player and the co-op campaigns are looking to be very good, though the multiplayer might not be very good after hearing this particular news.
Source.