Laurel Papworth tweeted: “oh noes! @lucasng we have to make a number up then. Quick Quick, someone give me a guesstimate of NUMBER OF AUSTRALIANS ON TWITTER!”
My guesstimate: 300,000 Australian Twitter accounts*.
Why?
Nielsen Netview, which uses research panels to sample the Australian population, reports there were 149,000 Australian Twitter.com users in Jan-09:

Meanwhile, Hitwise reckons Twitter.com was the 100th most visited website (measured by Australian daily visits) in March.

Hitwise also reports that from January 2009 to March 2009, Twitter’s market share of visits has more than tripled.

Using the Nielsen figures of 150K as a starting point and looking at the January to March growth rate in Hitwise, I guesstimate that there are probably ~300K Australian Twitter accounts as of March 2009. Note that the Hitwise figures don’t account for Twitter API access.
So that’s pretty darn impressive but let’s compare Twitter with Facebook and Mysapce, the big two social networks:
- Facebook: 4,821,580 active users (source: FaceBook Advertising - as of 23rd March 2009)
- Myspace: 2,362,000 unique browsers (source: Nielsen Netratings, Jan-09)
- Twitter : ~300,000 accounts
Twitter is in the media everywhere and has a high awareness (then again, so did Second Life, ugh). However, it has not quite reached mainstream usage.
Do you agree or disagree with my back-of-the-napkin calculations? Will Twitter become a mainstream social network and/or medium for communication?
Note: Standard measurement disclaimers apply. We’re comparing apples to oranges to pears with regards to users, browsers and accounts.
*edit: made some adjustments after @problogger got an updated chart from Hitwise, showing Twitter.com has gone from 100th to 85th most popular Aussie site.