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.