I never understand the published twitter numbers. The article says there are half as many twitter users as facebook users, but I know very few people (probably less than 1 in 10) that use twitter whereas almost everyone uses facebook.
Worldwide, twitters user count is rather small compared to facebook.
Also, with the numbers they have, we should be in the top 10 twitter countries in the world, but I haven't been able to find South Africa on any international list.
I wonder if they are counting actual users or users that have clicked a link from a news article that opened a picture posted on twitter, etc.