The biggest problem, which does not at all make the system impractical, seems to be the availability of working bikes and open docks at the stations you choose. The city (Montreal) seems to have trucks that go around and redistribute bikes fairly often based off of the real-time data the stations give them. Still, there have been several situations where during peak hours there are favorite "pick-up" and "drop-off" points, meaning there are no bikes for you to pick up, and if you do get a bike, there is no space at the station where you want to drop it off. There is usually a bike or two that's broken down at each station, so it's important to put every bike through a few tests to avoid frustration.
For me, the times that it was the most useful was either to commute, supposing a bike was actually available, or to get home after a late night out after the metro has closed. I hate taxis and will only take one at last resort, it was awesome to just take a bike back home.
I overall liked it but it's difficult for me to justify the added cost, since I'm not about to get rid of my metro pass. I would probably end up saving money if I replaced my pass with bikes and packs of metro tickets if I really wanted to, but that would not work during the winter when the stations go away.
Let's take Toronto. I could probably bike to work 9 km in an hour (half an hour if I had a dedicated lane - but I don't). However, in summer I sweat a lot and there are no showers at work. In other seasons - it is rain and snow that are the obstacle.
http://www.brisbane.qld.gov.au/facilities-recreation/sports-...
The only downside is the small diameter of the wheels makes climbing a bit comedic.
Wheel diameter doesn't matter for climbing, though. Bigger wheels are more efficient on a flat surface by way of less rolling resistance; the bigger wheel creates a smoother tangent with the road surface, and contains more air so deforms less under its weight load. But when you're climbing, rolling resistance means almost nothing compared to the energy you need to supply to climb the well of gravitation potential.
The problem with climbing on a folding bike is frame rigidity. The geometry required by most folders (long single tubes connected by joints with necessary slop for folding) means that a fair bit of the energy you supply goes into stressing and flexing the frame rather than transmitting into the drive system. The traditional brazed diamond frame doesn't have that problem. To make an extreme metaphor, climbing on a folder is a bit like pushing a string, where the energy goes into deforming the nonrigid body instead of moving it.
If wheel diameter mattered for climbing, then either skateboards couldn't climb hills or they'd have bigger wheels for doing so.