I bought one but never used it in my M45 - got really lucky.
Everyone here will tell you to get an Infiniti Elite. May want to check out the thread some one started about what you ought to pay for an extended warranty - I checked out prices at a few Infiniti dealers: Infiniti of Scottsdale used to have some of the best prices for it around, but that is not the case necessarily. I think I checked out a dealer on the east coast and they came in a few hundred cheaper. The prices go up with the more miles you have on your ride and for the length of time/mileage you want coverage. I intended to get one before 60k on my M37, but I blew by that milestone awhile ago - will need to look at prices before i hit 70k
You have one electrical thing go wrong on your car and the warranty should pay for itself.
here's the thread:
m56-aftermarket-warranty-t608739.html
FWIW, my wife's 2012 Durango's extended warranty was through AUL - they've been great: had to replace the entire small block at around 52K, coolant leak, cylinder head warped...probably over $5000 in parts/labor/rental car fees. Didn't pay a cent. Bought the car used as 26k, about $1400 for a 6y/100,000 mile warranty...