'Shared space' is a concept put forward by some infrastructure developers. The idea is that traffic signs, traffic lights and traffic regulating paint on the road are removed as much as possible and there is no separation of road and sidewalk. Instead of signs and restrictions, the road users themselves work together to regulate the flow of traffic.
Shared space is not popular with most cycling infrastructure enthusiasts. Cars remain intrusive and threatening, making the roads unpleasant for cyclists and even more so for pedestrians. Shared space proponents state that good shared space design invites car drivers to be more gracious and careful, but a minority of dickheads will always remain, and as a cyclist or pedestrian one always has to take the possibility in account that the next one will be one of those, and not one of the decent majority.
Still, I think there are some situations that are, at least, very similar to shared space, that are working quite well. One of these is in the center of my own city, 's-Hertogenbosch. Like many Dutch cities it has a large shopping center that has been almost completely pedestrianized. However, in 's-Hertogenbosch this pedestrianized area has been opened for cyclists as well. It's a shared space, without cars, and it seems to work. One cannot speed through it on one's bike during shopping hours, but I have never seen anyone trying to do so, either. A similar example, this time with cars, is found in several 'woonerven' (living streets). Some of these are just traditional streets with a sign, but others are very shared space-like in their appearance.
Why do these examples work, and 'normal' shared space not? I think it is because they do not try to treat all types of traffic equally. Rather, they are designed for pedestrians first, and car drivers and even cyclists are guests. Not without reason, pedestrians and cyclists are called 'weaker' traffic. If a street treats everyone equally, the result will be that the most powerful traffic elements will be boss. A working shared space design is one that turns the power base around: Give a lot to pedestrians, some to cyclists and just little to car drivers. Cars will still be bullies, but they will be bullying to get their fair share of the road rather than to deprive others of theirs.
An important aspect of this 'pedestrians first, cyclists second, cars merely allowed' design is to reduce the number of cars, by including elements of filtered permeability. Those roads should not be through routes by car, and not major through routes by bicycle.
Put pedestrians first, reduce the number of cars. That's how you can make shared space to work. Then again, if those are done without shared space, the result is great already. In the end, shared space is then just the icing on the cake.
Relevant link: David Hembrow on nearly car-free areas