I don't think D really helps a lot with fuel consumption. It puts too high gears too soon. I drive it like a Manual most of the times. And either use the paddles or the gear lever.
I use D most of the time. I find going to manual mode too much effort for a daily commute. It's different to a manual, in that it's second nature to change the gear, whereas it's not the same for the DSG. You have to actively think about hitting the paddle. Hard to explain.
Plus, when coming to a stop in D, the downshifts are much smoother. In manual mode they can be a little intrusive. Probably because the car is waiting for you to do it, and leaves it to the last minute to intervene.
Full manual when I'm going for it though. Sport mode is pointless for me.
As an aside, have you guys used launch control? Thought about it, but I can't see it being too kind on the longevity of the box.