1. Religion isn't a big cultural thing here. Coming from the Bible Belt (Springfield, Missouri) where religion is a part of every day life, this is a huge difference. When we lived in Springfield, there were many times I would meet people and the first question they would ask was "what church do you go to?" I was even approached while getting gas by the guy at the pump next to me. He wanted to know if I had a "church home" and invited me to his. Not so in Melbourne! I read that 80% of Melbourne residents do not attend church, nor do they affiliate with any particular church. I've seen quite a few churches here, mainly Anglican or Uniting (still not entirely sure what that means) and one Baptist. But these churches are old and beautiful and seem to serve as a tourist attraction and architectural spectacle more than anything else. This is a sweeping generalisation and I have yet to know anyone well enough to ask about their religious beliefs, but my opening when meeting Australians probably won't be "what church do you go to?"
2. Things are more laid back, but not inconveniently so; stores are generally open regular hours and won't spontaneously close in the middle of the day (cough Europe cough). They do close pretty early, though, and even though we live in the center of the city, it can be a struggle to find restaurants open later than 7 or 8 on weekdays. Except for McDonald's, of course, which is still open 24 hours here! People in general have a laid back attitude. "No worries" is an Aussie's favorite phrase and they really do use it sincerely and abundantly. This can work to our disadvantage though, as people aren't in nearly the rush to get things done in a timely fashion (ie. the main light in our living room that has been out since we moved in and is no closer to being fixed). It's an exercise in patience.
3. Although you drive on the left side of the road, it's not abundantly clear that you walk on the left side of the sidewalk. We are constantly dodging people and trying to figure out the pedestrian traffic patterns to no avail. I think it's just kind of a cluster in the city with so many people.
4. Australians don't seem QUITE as attached to their cell phones (mobiles, here) as Americans. Sure, everyone has one and people are generally using them on the train or walking down the street, but I've noticed in groups and at restaurants people usually ditch their phone in favor of actual conversation. What a concept.
5. Every Australian dreams of visiting the US. Ok probably not every single one, but 98% of the people who find out I'm American (and haven't already visited to US) say "I've always wanted to visit America!" They also can't believe that Americans are just as enthusiastic to visit Australia.
6. Personal space is not a thing here. You can be on the train with practically the entire car to yourself, at least 50 seats open, and someone will come sit in the seat next to you. At restaurants there are often long tables and you'll just sit down next to someone else. It's a little weird to get used to.
That's about all I can think of for now!