Twitter has made headlines for some amazingly powerful stuff lately; breaking the news of recent Chinas earthquake; partnering with MySpace for its data availability project; even helping a student get out of jail! All of these speak to the growing popularity of Twitter, and also help to explain its recent scaling issues. But how big is twitter, who uses it and how?

Growth a tween would be proud of.

In the past few months, Twitter has grown rapidly. In terms of U.S. visitors, Compete has seen Twitter traffic nearly double from February to April, currently attracting nearly 1.2 million people per month. Looking at Twitters Attention share helps to further illustrate how fast the service has grown.

The chart above shows Twitters share of daily attention for the past 180 days, and reveals some interesting patterns.

In terms of time spent on site as a share of all time spent online, Twitter has grown dramatically - more than quadrupling over the period. Twitter is a weekday event While its difficult to tell in the chart above, the valleys in the chart below coincide with the weekend, while the peaks represent weekdays. On any typical weekday, Twitter is receiving more than twice the attention as a weekend day. The weekday skewed tweet activity makes sense in the context of Lee Oddens Twitter usage poll - which highlighted twitter users affinity for networking and sharing content through twitter.

Its fun to hang with the Y.M.T.A

Who are these 1.2 million visitors, and how intensely do they use the site? We segmented visitors by intensity of use, gender and age for the month of April to get a better idea. Generally, users skew young, male, and addicted to twitter.

The data above shows that nearly one quarter of all twitter visitors to the site are heavy users (6+ visits/month), and another 25% are light users (2-5 visits/month). It should be noted that the somewhat lenient definition of a heavy user was a result of the many ways user can connect to Twitter.

The gender and age breakdowns indicate that users skew young and male. These two charts are indexed to the U.S internet average, where 100 is the average.

Twitter users are 10% more likely to be male than the average internet user. This skew is nearly identical across all three Usage groups. Twitter skews heavily towards the college/twenty-something crowd. Twitter attracts 18-24 year-olds at nearly twice the rate of an average U.S website. Splitting age demographics based on usage intensity shows that heavy users tend to skew older than visitors who only hit the site once a month. This could indicate that while the younger segments are more exploratory, the 25-44 year old segments have found more value in Twitter and started to ramp up usage.

Twitter may be growing like crazy but its yet to go mainstream. Interestingly, Twitters strategy of letting developers re-purpose its data may help the service reach the tipping point by making Twitters value more accessible. Check back next week to see how these twitter based sites (like twitterlocal and summize) are building a loyal base.