If you long for the handling of a world class sports car, yet need the practicality of a 4 seat car, the M3 is for you. I bought the newly released M3 convertible about one year ago and absolutely love it.
When looking for a new car I had two criteria, a sporty convertible and seating for 4. Several other cars fit the bill, including the Saab 9-3, the Mercedes CLK, and the Volvo C70, my reason for picking the M3 was pure handling and driving excitement. The M3 with 240 Hp has good acceleration, but it really excels in the turns. There is almost zero body roll and the large sticky tires keep the car completely glued to the road. When the car begins to slide in a turn, all four tires slide evenly because of the even front/rear weight balance. I spent the first several months just trying to get the car to fish tail once. (I finally did it at 45 mph on a sharp turn in the rain at full throttle)
After buying the car, I took it to Dinan motors for some slight modifications. Dinan replaced the shocks and structs and reinforced some suspension joints. They also added a cold air intake, strut tower braces, new engine control chips and a free flow exhaust system. For an extra 9K they can also add a supercharger which brings engine output to 350 Hp, but I opted out because it voids the engine warranty.
I highly recommend purchasing the rear wind screen accessory, it clips into slots over the back seat and reduces the wind coming into the front seats down to a slight breeze up to 75 Mph.
My complaints with the car have been that it is way too low to handle city driving and many driveway curbs, look out for those speed bumps, the transmission scrapes many of them. I also dented two rims on a pot hole, which cost $400 to repair. There is some cowl shake when going over rough spots or rail road tracks, but the shake is much less then the stock 3 series, it appears that the Motorsport engineers significantly reinforced the frame over the 328. The interior is nice, but not really up to the price tag of this car.
On the positive side, the back seats are actually functional, with enough room for a full size adult, just slightly cramped. The trunk is small, but way bigger than the "roadster" convertibles. The top is fully automatic and very quite when up. The pure pleasure of driving an open top car with the power and handling to zip through traffic or coast down winding roads makes every penny spent on the car worth it.
update: (Sept, 14)
I scratched the right rear wheel again, parallel parking in the city, ugg. I just can't bring my self to think about getting a different car, there just isn't any substitute for a convertible on a nice open highway...
latest update: (Oct. 28)
The rainy season came a little early to California this year. I had to put the top up for the first time in a month. Did I mention that plastic rear windows are not perfect? Otherwise the car is still functioning perfectly. I'm not sure, but it may have gotten even faster after the first 12,000 miles, it sure feels that way. Now that the tires have some wear on them, the car can slide a little bit in turns, it makes for a lot more excitement, but it's never scary. The car just seems to float a little and slides very evenly through a turn at full acceleration. I think that new tires will be necessary at 20K miles.