Gave them a go last year - was impossible to get a taxi or ride share accepted. Seems like the google+ of these apps (a ghost town), likely just created to turn people off using any of these apps. Will be good when lyft and others come to town.
I used GoCatch a few times earlier this year to catch a taxi - most times I was able to get a taxi, but a couple of times I was in the middle of the city with taxis flying past, but nobody accepted within the app. I would delete it, but in QLD the lower CC surcharge through this app (plus the benefit of QFF points and electronic receipts) makes it worth it.