The G-35 is built on a 350z, stretched, and with a transfer case in the event of AWD.  I could pull that car apart piece by piece, and reliably re-assemble it blindfolded.  There's no way to get warranty coverage without going over the hill, but if your concern is simply having a mechanic who knows the car, you're covered dude.  
As far as the platform overall, I've always liked the G, as a whole, more than ANY other Nissan vehicle currently in production.  They're VERY reliable; well built.  There seems to be better quality control with the Infiniti brand.  I've personally seen a only little silly shit as far as frequent repairs go, (seat switches, the occasional fuel level sender...) but I've never seen one with a big dollar or catastrophic failure (engine, trans, etc.).  
This may seem un-noteworthy since I work for Nissan and not Infiniti, but keep in mind that the first place local Infiniti owners go when they have a problem is HERE.  I can see 3 of them right now sitting at my computer.  An I30, a QX4, and a G35 coupe.