Maybe every city is like this and I just never noticed. But I don't think so. There just seem to be squillions of them. I get the impression that Perth really punches above its weight in this regard.
Not sure why it would be this way ... Perhaps it's got something to do with the outgoing, optimistic and highly social culture of the place combined with the booming economy. Unlike other major Australian cities there are many people earning very good money here who can afford to dine out regularly in pricey local restaurants and cafes. Clearly, anyone servicing this market who is not on using social media is missing out big time.
And just as today's online technology is facilitating the growth of traditional hospitality businesses, it's giving rise to new ones such as aggregate review sites. This well established model includes Bean Hunter and Urban Spoon. But online entrepreneurs can be much more individualistic and localized than that.
For example, you could build a site totally focused on Perth cafes. You could include photos and videos of your favourite ones and publish interviews with local baristas, etc. You could have a blog that included comprehensive cafe reviews along with related news updates and even gossip. Such specific content would be ideal for sites like Twitter, Facebook, and Pinterest. With a decent following you could monetize it with related affiliate programs as well as paid advertisements.
If you kept at it there's no reason you couldn't become the go-to guy for advice on Perth cafes. You could then leverage this new found authority to score gigs writing for mainstream media.
Another approach would be to build a site selling coffee beans and related products such as espresso machines to local cafes. Knowing how many of them are already tweeting and pinning up a storm you could use social networking sites to attract potential customers in a very short space of time.
And how about a temp agency for cafes? Every day in this city there must be numerous cafe owners pulling their hair out because of staff no-shows and cancellations due to hangovers, etc. Social media would be a fast and effective way to get on the radar of such business people -- not to mention organize prompt staff replacements for them.