I personally feel that its great where the world can connect and talk about a single topic and share their experiences maybe also. We get to "sit" down and chat about it, however sometimes there might be arguments and cyberspace fighting when the things we chat about starts to get a little too biased or no-proof thing.
One con about WallWisher is that we are limited to only 160 characters per sticky, which is bad when we want to write long statements. You may then put an indication like "continued" or "..." to show the continuation with another sticky.
And for example, as a school or class, we can use WallWisher to discuss about whether a learning thing or CCA and our opinions would be able to be seen by the world. (you can change the settings btw)