I've spoken to a few webmasters here who have said they're yet to join it. They say this is because even though it looks good there are hardly any other Perth people on it.
True, it hasn't really taken off yet in Australia. But it certainly has done so globally. So, slowly but surely more and more people in this country will sign up and get involved.
This is one of the reasons why it's a good idea to get into it now. You'll be on the ground floor, so to speak. You'll benefit from the momentum as people keep joining.
I've noticed this with my own personal account. Over 600 hundred people have me in circles already. And every day, new people are circling me. While some of these are returning the favour after I have circled them, most have not. They're just finding me from my activity on the site -- particularly in the communities.
On that aspect of Google+: People are very engaged in these discussions. The quality of information exchanged is high, certainly better than in Facebook groups and even on the same section of Linkedin.
If you intend signing up, that's where I would put most of my energy at the beginning. Discussions are a great way of getting seen by lots of other users. You can participate in them as yourself, or as your business. (This is a real advantage over Facebook. On that site, business pages are not allowed to join the groups.)
Unfortunately there are only a couple of locally oriented Google Plus communities now. But there will surely be more in time. And there are numerous globally oriented ones that are immense and going gangbusters. Participating in them will help you grow your network quickly.
With lots of quality people and businesses circling you and receiving your updates you'll rack up those valuable "plus ones" at a faster rate than you would normally. Your engagement with them will hugely increase the odds of getting voluntary one way links from relevant websites, too. Both these things improve SEO.
There are other search benefits that this network can bestow, particularly when it comes to local optimization. Then there are the many advantages of authorship markup.
If you're in this city and have a business, taking in active part in this brilliant social network is highly recommended.