For me:

There's turbo-lag for the first 1/2 second, if I floor it from a stop light ONLY. I've only done this a few times, though.

It's relatively noticeable, but partially due to the fact that I'm specifically looking for the "lag." Is it more noticeable than any other turbo vehicle I've driven? No, it's really about normal, and I've driven many turbo vehicles throughout the years.

Sport Mode tunes the Adaptive Drive Suspension (shocks and roll bars), not the engine timing, turbos, etc.

I'd say the lag is on the minor side, and curiously it does not always present itself, but again, I've only specifically "tested" the vehicle for lag a few times.

I have about 2,900 miles on my 35d. There is zero lag, that I can notice, when flooring it at 60 miles per hour or at 75 miles per hour up a hill, etc. There's simply a VERY smooth progression of thrust, as if the turbos are already spooled up and are instantly at my beck and call.

Again, for me, the only lag I get is when the car is at idle, and I'm accelerating away from a stop sign, and to repeat it's only sometimes that I get that. At other times, it's as if the turbo is already spooled up and expecting my command.

That's my experience in a nut-shell, which encompasses 60-hours+ behind the wheel of the 35d.