I have a 2006 Cooper S convertible 6 speed and my entire family loves it. The back seat is a good size for young kids (6 and 4) and the storage space is adequate for a week's grocery shop. I can't believe how much fun this car is for the price. In fact, I can't think of a car in this price range that's as much fun. We've only had it since February. Bought it at 59000 miles, it now has 67 and the only thing I've done is change the oil (easy to DIY if you have a 36mm socket for the oil filter housing, which I do from my 915 rebuild). I've taken it to the track, where it proves that, at the end of the day, it's not in the same league as a Porsche, but I still had an awesome time understeering it around the corners.
The convertible top is nice and easy to operate, and it's one of the few cars whose lines aren't totally ruined by the convertible top - the lines with the top up are very similar to the coupe, and the opening is half the size (fold down tailgate). The only downside to the ragtop is you do lose some storage space in the back compared to the hatch. In a coupe, I can fit my entire guitar rig - 4x12 speaker cabinet, combo amp, 2 guitars and a bag full of cables and stuff. I can't do that in the convertible because the opening isn't as big.
Our 3rd car is always a temporary car - I buy a car through work, drive it for a year and sell it at a break even. When I sell this one in the spring, I'm most likely going shopping for another one, exactly the same. How's that for a ringing endorsement?