SMG was a single clutch, computer controlled manual. It's similar, but not as complex as the modern, dual clutch setups. I've only driven the Ferrari F1 single clutch setup, and like you said, it really only works right when given the boot. It was unbearable as a daily driver, especially in stop and go traffic like on the 405.
There are a few E60 M5's with six speed manuals around, but they have non defeatable stability control. Pity. Such a glorious engine with such a turd of an auto-manual. I've just written off E6x M cars because of the SMG.