I talked to a service manager about this issue today, and he said with a straight face that they haven't had a 350 need a transmission replaced like this yet. I know they're liars (I even told him I figured he wouldn't tell me if they did have problems), but it's a data point.
I'm still worried about it, mostly because I want to put in a short shift kit, which might create warranty issues (see my post here
Installed B&M 45163 short shift kit in 370Z yesterday...).
The service manager did do the usual snotty thing and say that a car that needed five transmission replacements probably had driver error, and went on to talk about people who needed a new clutch at 10-12K. Personally, I don't see how anyone could drive a car poorly enough to go through transmissions at that rate, unless they were trying.
Anyway, this sucks. Does anyone have any numbers on the percentage of 350s or G35/37s that were/are having this problem?