I've had no lag and I have what feels like the worst connection in Britain. However, I have been disconnected once and lost a decent item I'd just picked up
Not the end of the world, but it seems bloody stupid that you should have to worry about being disconnected in single player. They'll fix the teething issues in no time so I'm not bothered, the game is as awesome as expected. It's probably got more people trying to hammer it this week than WoW, I'm not surprised they are working on balancing servers.
If anyone wants to add me and party up it's Clocked0Ne#1951