I've owned a couple of convertibles and loved all of them. Unfortunately, none were Mustangs.
I eventually gave up on convertibles based mostly on the fact that I live in the northeast and can only put the top down on a regular basis for less than six months per year. I still like convertibles and admire the late-model Mustang models, even if I don't plan to buy one.
Maybe its just me, but I've always believed that even the most ugly car (say, a VW 'Bug') always looks a lot better when you have the convertible model - with the top down.