I've had the car for 5 months now and couldn't be more pleased. The car handles exactly like you would expect and has outstanding performance. I have the 500 convertible and it doesn't accelerate, it leaps forward. I can imagine how the '07 550 accelerates. I compared it to the Audi S4 and the BMW 6 convertibles. The only thing the Audi had on it was all wheel drive - but it came with a higher monthly lease cost. The BMW wasn't as attractive and the back seat was not worth having. The back seat on the Benz while not expansive can and has held 2 full size adults confortably. The convertible top works great although it could be a little faster and less sensitive to items in the trunk.
Upgraded sound system, convertible, seat coolers.
Improved radio controls on the steering wheel. Make the on board computer/driver info system easier to use.