The content that is created in many Wikis is really relevant. Wikipedia for instance provides you with unsurpassed encyclopaedic type of information. This popularity can be deduced by Alexa's current ranking for today .. number 9. For us users and editors of Wikipedia it is like a roller-coaster; it is exhilarating :)
For people who are visually impaired, several of the Wikipedias have projects where people record the articles .. Really nice, really relevant.
Today I learned about new software promoted by UNESCO called Sakrament Libreader, it allows for text to speech conversion for English, Russian and Belarussian. Just consider, the English Wikipedia takes, according to Alexa, 53% of our traffic. There is a certain percentage people that are visually compared to the unimpaired.
Consider what would happen if the Wikimedia Foundation would support and promote this kind of functionality. Not only would many people be helped by this, it would also give an impetus to make this functionality available for other languages..