I surprised my wife with an M45 last month for her birthday. She absolutely hates the car. She complained from day one about all the technology the car has. She can never get the A/C or radio to work right, the navigation isn't even an option for her. She says her 2002 Lexus GS430 had much more user friendly controls, my son now drives that car. I have been driving the M45 the past few weeks. My wife has stolen my 2006 Lexus GS430. Although it has most the features there much better placed and a lot easier to use. I have no problem with the M45. I wish I would have had her drive the car first before paying cash for it. I'm happy with the car, but would prefer my Lexus. In January I will be trading it for the LS460.
Rather than getting an infiniti, spend the same amount or a bit more and get a lexus or benz, which have proven quality and you will be happy.
Mercedes-Benz E Class cars have not had good reliability for several years now, although that is allegedly changing. The Lexus GS cars, while luxurious, are simply boring to drive.
My GS430 has 300hp and 325tq, to the rear wheels, and a 5-speed auto tranny. 0-60 in 5.5 seconds... not boring.
That being said, the M35/45 is an amazing car. Cars I have owned or test drove:
Acura TL (owned)
Celica GT4 (owned)
Lexus GS430 (owned)
BMW 325i / 540i
Audi A4 / S4 / A6
lexus GS300 / GS350 / GS450h / LS / IS / RX
Infiniti Q45 / M35x / G35
I am a car fanatic, and the Infiniti M35/45 is second only to the Lexus GS450h.
It's personal. I drove Lexus GS430 and I agree it's boring to drive, I feel myself like I'm on retirement even though it's still powerful enough, but feels fluffy compared to Infiniti M.
I own 2007 M35, and I'm in love with it. Before the M I tried many different cars (Acura TL, TSX, Hyundai Genesis 3.8, Merc E350, G37 Coupe, G35, Q45, Ford Taurus SEL Limited, Subaru different models, Honda Accord, BMW 325, Lexus LS430, ES350, IS250, GS430, Nissan Maxima 3.5, and so on). The G35 is more powerful, but the interior seems much cheaper compared to the M (smaller ash trays, window controls are closer so I need to move my hand far back to reach the front window knob, much less space in between seats) while the engine and 7-speed transmission were just impressed. So my vote goes to Infiniti M, and my next car will be 2011 M37.
Lexus is good and almost common. Mercedes Benz is a joke anymore, not the cars of the 70s and 80s. They have a cheap feel to them. Mass produced. Infinti makes a good product, it's something different than a Lexus and a little cheaper.
Hey it's your money, buy what you like.