Yes! Lan party games are awesome! Especially when you have 8 guys playing Halo, four in one room, the other four in the other, throwing banter at each other, trading players, and these are all guys you know. It goes from being a "One screen per team-player" to a "One-screen team"!
Or having a room full of computers with each running a copy of Warcraft III or Starcraft. It makes the race to own the map that much sweeter when you finally crush one of your opponents, just to have him come look over your shoulder to see how you did it.
Oh, and I guess that the DS' wireless connectivity to other games in the area would also technically be Lan, cuz you are connected, and not by the internet.