Easy usage is the most important thing that we can include if we want to have an impact on the world. Why would people take the time to read an extensive manual for a new machine or development? This is why, on top of trying to create cheap solutions to the problems, we need to make them simple and transparent so that their use can spread. This way the people who are using it will be able to explain it to their neighbors, which will be vital to the success of whatever new invention we provide. A good example of this is Michael Pritchard's water filter (http://www.ted.com/talks/lang/eng/michael_pritchard_invents_a_water...) which turns filthy water into pure drinking water. The easy use of this filter will create a low threshold for strangers to this filter, saving more lives with every new introduced filter.
The easier life becomes, the more people will want to share in this ease. Simple is the way to go!