Loved my smg m3 while on it.
However after a few months of commuting 60 miles a day I was getting tired of it. When it auto mode you do have to think about it all the time and its slightly un natural.
There are horror stories you read of smg pumps and so on but I never had any issues over two e46 m3 smg cars I owned.
If I was to buy another e46 m3 i would probably go manual next time if it was not a weekend car