a de.licio.us toe-hold ?!?

Used de.licio.us to get a toe-hold really, it didn't seem that easy to find good information, there was such a lot that seemed irrelevant.
But it narrows the search and once I found a good link there were better links leading from that.

So I found:

http://www.web2fordev.net/component/content/article/1-latest-news/69-social-networks

Only 14 out of 50 African countries seem to have members on social networks. Although as we found in our examination of internet use in developing countries, access and use in Africa tends to be patchy and concentrated.

According to Appfrica (http://appfrica.net/blog/2009/03/04/facebooks-africa-numbers/), South Africa has 1.1 million Facebook members, Morocco 369,000, Tunisia 279,000, Nigeria 220,000, Kenya 150,000 and Mauritius 60,000.

The UK has over 27 million users (June 2010), Europe 101 million (Jan 2010) and Africa 9 million (Jan 2010) (ref: http://www.clickymedia.co.uk/category/blog/social-network-marketing/facebook/).

Facebook is obviously not the only SNS - a breakdown of primary SNS usage by country can be found at: http://www.vincos.it/world-map-of-social-networks/

Language can be a barrier to entry.

The importance of using mobile phones for access is highlighted.

I didn't find anything specifically about various income groups, I'll be interested to see what others find.