I too will be getting the BRZ and if I end up getting a MT, it'll be my first MT. I've driven my girlfriend's dad's ford fiesta to learn a little (maybe 4 hours), and I feel that I've got the basics down. However, I still fear driving in traffic because I know that driving in traffic is not the same beast as doing it in an empty parking lot. ESPECIALLY with other people who can potentially be terrible drivers. It is a scary feeling to be out there knowing you're not the best you can be in your driving skills due to the MT.
My father who's driving MT for a long time, and is a car enthusiast, suggested to me that it is something you have to own to be able to master it, and like everyone else says, it becomes second nature. Kind of like riding a bike
I'm actually looking forward to it even though where I live (tallahassee) has some steep hills and crazy stop and go traffic all day long.
Can't wait to hop on the interstate and just drive fast