BMW bills itself as creating the Ultimate Driving Machine. With their M cars they certainly live up to the billing. The handling is superb, the acceleration is swift, but it has the gas mileage to match. Do not buy these cars without consideration of the increased costs of higher octane fuel requirements, more expensive tires, and higher maintenance costs.
My wife loves the car, it's lines and styling are beautiful the comfort and ride are great, the X5 performs great but it does love that super unleaded though. My wife doesn't drive to much so we are not affected by the low mpg this bmw gives. This is not a car that a person looking for fuel economy should consider(it is a thirsty little bugger)especially in these high fuel price times it (will run you between $73.00 & $88.00 to top off). So if you like to drive lots & lots of miles and you are concerned as to how much it cost to top off your tank stay away from this car. If fuel economy and money are not a concern stay away from this car.
2008 M5-- I needed a car that I could have a blast in, as well as take clients out in, or my family (wife and 3 girls). I chose the M5 over an E63, CLS63, and the CTS-v. CLS backseat is unusable, E63 is not as fun to drive, in my opinion, and the CTS-v-- although it is an unbelievable car, it is just too small for my needs (primarily the back seat). The styling is understated, with only the purist able to recognize what they are looking at. I am not a flashy guy, and do not like to draw attention. I bought this car for me, not for others to look at me! I love the fact that it will not turn heads unless someone is an enthusiast that recognizes the 'M5' logo. Interior redesigned slightly from the 06-07 model, and I feel it is much better than the previous interior. Drivetrain and major components unchanged from 06-07 model. V10 is incredible-- fantastic sound, fantastic powerband. It does sound slightly tinny when cold-started (read owners manual), but in "power" mode and full throttle after warm-up, the sound is amazing. SMG transmission is not for everyone. I personally love it (11 different shifting options, F1 style shifts, it blips throttle on down shifts, launch control), but it can be rougher than other traditional automatics out there. I-Drive is very capable, but not very intuitive. It will take a while to become proficient at using this interface. Once you are somewhat used to it, it is less annoying. I personally do not think it is as bad as its reputation. Car drinks gas-- but if you want an economic vehicle, you are probably not even reading about an M5! I average 15 mpg, and do a fair mix of highway and city driving. The interior is very logical, and extremely comfortable. The car has a very "expensive" feel to it. The heads-up display (HUD) is a must. Navigation info, cruise control info, speed, tach, gear selection information all on your HUD. I have rear-heated seats, which are NOT a must! Also nice, but not needed are the heated steering wheel and soft-close doors. The ventilated seats are not on my M5, and that is the only thing I regret not opting for. BMW offers a service plan which is a must-- it will save you about $1500-$2000 in maintenance costs over the term of the plan. Extended warranties are pricey through BMW, but remember this *is* an M5! The Drive-- This is my third higher-end performance sedan, and I must say it is the best car I have ever owned. The power, the balance, the unlimited set-up options-- all come together to deliver the ultimate drive. Not to mention it is smooth as silk when I need it to be (taking clients out, for example), and it is always a conversation piece for the drive to lunch! Good luck with your search, and keep in mind that you cannot go wrong with the M5!