Lag depends on how many people are playing and how far apart the players in question are. If you've got a 3v3 with players from all over the world, you're going to get lag no matter what.
I do not wish to contradict you, by abusive generalization, based on one single example -- especially since I'm no expert on "lag".
But this situation occurred to me, yesterday evening, playing the beta update.
I entered a 4 v 4 on Leviathan. We were 2 North Americans, and the other 4 were from Europe (France & Germany).
During the game setup, I noticed that all of the pings (except the one from the US) were between 150 ms and 200 ms. That was a new type of situation for me, since it is rare that I play with people who exceed 150 ms.
Well, believe it or not, there was no lag, except for a few brief pauses. One guy dropped out, and my team won (despite having a replacement bot on it).
Next, I entered a 3 v 3 with other Canadians and Americans. Nobody, at the beginning, had a ping above 150 ms. The game lagged badly : we had to abort it.
I know it wasn't because of me, since I have a fast & very stable cable-connection. (I often download huge game-files from Impulse, GamersGate & Gamespot at a steady 850 to 900 kb/sec.)
I don't know what to think. One hypothesis is that some careless gamers download stuff in parallel to playing DG. Consequently, their connection, even if it is theoretically fast, will have ups & downs, and all those activities cause interference.
Before I launch DG, I close as many user-defined processes, in XP, that I can. When I'm playing DG, I do just that : play DG.
People who alt/tab and check on their other programs, which are running in parallel, are selfish & careless, because they risk compromising the flow of the game for other gamers just to multitask for their personal satisfaction.