Just something I think I should point out here:
I've noticed that if there is ONE guy that has a really bad connection he somehow causes LAG for everyone.
There is an ingame warning stating which user is slowing down the game when this happens
Yeah I know...It's always YOU lagging!
The reason for the lag is because the B.net servers are overseas, so the signals take about half a second to go back and forth. Theres nothing you can do about that really.
Not quite true. The game is peer-to-peer, so if you play in a LAN against a friend via bnet, you'd get LAN speeds. If you join a random game, it all depends on who you are playing against and how good their connections are. I have played many games now, and have only experienced bad lag in 4v4s.
Usually its one of the other players since its always showing "waiting for noob123".
Just want to add: Over the long weekend, 6 friends of mine were lanning SC2. My friend and I joined in their games and we played 4v4's lag free.
I play on MTN's HSDPA and I rarely have lag. I actually think the new netcode for Starcraft 2 is out of this world.