I had an M3 with an SMG II gear box (paddleshift) which was at the time 52 plate, the best auto type box in the world, gear changes in 180th of a second in its most ferocious mode. It was great fun for a while, but there is nothing like to control a manual gives you.
I was also unfortunate enough to have a FTO at my disposal for 3 months which had a tiptronic box, although that was very horrible and clunky.
However I have not used the tiptronic box in a Z, don't get me wrong, i'm not saying its the worlds worse and I don't have direct experience of that particular box, however in my opinion I have never driven a car with an auto box that can match a manual.
If I was driving 100 miles a day on motorways or in city traffic, then maybe its a different story, but for country lane driving, I think my point stands