Haven't heard of engines problems from members' feedback on here, but there have been gearbox issues with several being changed before the warranty expired (mine included). Without trawling back through those reported cases, I don't recall those issues coming to light in the first 1200 miles, but I believe the data will be there, if Nissan chose to check.
Personally I would respect what the handbook says about the running in period, which in the case of my 370 that now looks like a long term keeper I am glad I did .