If you were only testing it by sliding, it really wasn't testing the AWD. You were putting your ABS, brake pads, and tire tread through a good test, though. When you're stopping or slowing down and you lose traction, the slip light will start blinking which indicates the car is cutting power and using ABS on individual wheels to keep you from spinning out. All G35's will do this. You'll really notice the AWD vs the RWD on these cars when you try to start moving from a stop in snow, especially out of a parking spot or something like that. I've pulled out of spots as if I were driving on some bumpy pavement while RWDs spin tires and struggle to make it out of spots, or have to feather the gas at a stop light before they can finally gain some traction. It's pretty awesome when you can roll by guys putting along for traction

 

I've done 1/4 mile runs in snow mode, it starts off in 1st, and is on average .2 seconds slower.