Performance? Come on, this is the United States, the land of pot hole riddled streets and 70MPH Interstate highway speed limits. Who cares about lap times on a German race track? I don't drive on German race tracks? Do you?
The fact of the matter is most street "performance" in the United States is measured from red light to red light. In the land of reality, an aftermarket built sub-$20k DSM, Honda, Supra, Mustang, Firebird, etc. can eat most any "supercar" on a quarter-mile or less straight.
Still, I don't think anyone here is calling the GT-R a slow car. It is actually a rather impressive vehicle. However, lots of people are calling it an overpriced car for whatever various reasons.
There is also the aspect of brand prestige. The bottom line is Nissan is not a supercar brand. Nissan can churn out a 200MPH car, and it is still not going to be a supercar brand. Ford can churn out a 200MPH car, and it is still not going to be a supercar brand. Pontiac can churn out a 200MPH car, and it is still not going to be a supercar brand. Hyundai can churn out a 200MPH car, and it is still not going to be a supercar brand.
Conversely, Ferrari can churn out a 150MPH car, and it is still going to be a supercar brand.
You are coming across as equally defensive about the subject as we are supposedly being offensive. I can't speak for others, but I am more or less picking on the car because of how Nissan has opted to react to some warranty claims (think transmission), not because the GT-R is an underperforming vehicle.
I poke fun at Honda, but not because Honda builds a poor product. I could drive a Honda. I poke fun at Mustangs, but not because Ford builds a poor sports car. I could drive a Mustang. We each simply have preferences, and to be blunt, stereotypes about certain car brands and models.