As far as I know (and I could be wrong, but I have seen numbers along these lines) that no matter what Jeremy says, the current Mustang, year for year, outsells any other sporty mid size car in the world by a factor of 2 to 1. Now, I don't know what other cars fall into that category. Golf GTI? Ford Focus RS? WRX? Evo? Maybe only 2-door cars in that relative wieght class. What does that leave, the BMW 3 series? Saab coupe? There just isn't anything really (esp in a convertible) to compete with it, and certainly near it's price point, until the Camaro and Challenger come online. It's a huge car for European standards, isn't it?
That's another thing, it was also named the safest mid-size convertible in this country (US). I don't see how that's possible, given the 335i and CLK's and Saab's and Volvo's attention to safety. The Mustang doesn't even have rollover protection (hence the $1,000 padded steel rollbar I had installed in mine).
But, I'll say it again, for the money, if you need a convertible with a back seat, there is just no car you can buy that is so much fun to own with rear wheel drive and that kind of power. Your only other options (in this country) are the BMW and Mercedes, and with similar power and size and RWD they cost twice as much...