First up, "car share" is a misnomer. I'd consider that to be when you let people jump in the car with you for a journey. I'd class this service more as a car micro-hire.
It works like this. You pay a monthly subscription ($15 in our case) and can then hire cars for $6.60/hour plus $0.35/km (higher monthly subscription means lower hourly rates). Petrol is included.
When you want a car, you either log onto the web site and book a nearby car, or you phone up. The phone system is surprisingly useful, and there's normally someone around if you get in trouble and need to speak to a human.
Contention on the cars would be the most common question, and to be honest we've rarely had a problem. Sometimes if you try at the last minute, you might need to walk a bit further or find another form of transport. But if you plan ahead, it's no biggie. We booked a car last week for the four days around Xmas, in a nearby location to our place. Long weekends can be a bit tricky, though you just have to book a week or two in advance. It's really in their interest to ensure there's enough cars. There's also some useful utility vehicles available: a ute and a Tarago in Erskineville are particularly handy and cost no more.
The day rates, it should be noted, include 150km of travel (including petrol!) and if you do the kinds of trips we use it for, driving somewhere, staying there a few days with only a few short drives, then returning, you'll find the 150km included in each day more than covers all the kilometres used in the trip. We find it's good value, and unlike car rental companies, there's no hidden charges and you don't have to be alert for all their sneaky damage, insurance and excess reduction scams.
Now we live in the inner city, which is where most of the cars reside, so it's particularly good for us. The best thing you can do, Mary, is find a few more people out in Hornsby and convince them to promise they'll sign up if GoGet put a pod out that way. They've been pretty rapid with their expansion, and they're not averse to trialling a new area.
The problems with licenses are also a problem for us. I'm on my learner's permit, and basically it seems we're going to have to buy a car if I want to get enough practise in on my provisional license. That's a shame. GoGet are pretty responsive to requests for changes, so perhaps we could propose something like a higher insurance charge for provisional license holders?
As well as the cost savings, these schemes are great because of the convenience. Sure, we have to walk a couple of blocks to the car, but we don't have to book in services, rego, insurance, repairs and all that. For me, that's the best thing about it -- my life is busy enough without having to deal with all that!