These figures don’t even take into account usage of Twitter—much of which comes via mobile and PC/Mac clients such as Tweetdeck (one million users and counting) which allow users to update without visiting Twitter.com using the site’s API. The study therefore ignores the most committed and engaged users—many of whom work in the media and PR biz and Tweet in a professional capacity and are exactly the kind of people that could be persuaded to pay for a more prominent presence if that’s what Twitter decides to sell.

SEE ALSO: Twitter ‘Bigger In UK Than US’, White Van Man Taking It Mainstream

—Traffic driver: During May Twitter was the 30th biggest referrer to other sites in the UK, accounting for one in every 350 visits to a UK site. It might not sound like much but some people do use Twitter as their personal RSS feed and Twitter was the 27th biggest referret to news and media sites in May. Twitpic, the picture posting service now integrated into many Twitter apps, was the destination for one in 13 downstream visits from Twitter—making it the third biggest UK photo sharing site in the UK after Flickr and Photobucket.

—No e-commerce boom: The research found that 60 percent of Twitter links send people to news, entertainment sites and blogs while only 9.5 percent are to online retailers or e-commerce sites, something Hitwise resarch director Robin Goad raises as a cause for concern. Although his comparison to Google (NSDQ: GOOG)—which sends 30.7 percent of outbound links to “transactional” sites and unlike Twitter does have copious paid-for advertising links —seems odd given the hugh disparity in the two companies’ models.

Meanwhile—Tweetdeck, which launched its iPhone app last week, has added a “Tweetdeck reccomends…” column which suggests people users might not be following. Instead of Tweets, the column shows people’s brief biographies to prove their relevency. Founder Iain Dodsworth told me in an interview last week the service would move towards recommendation—and even monetise it somehow eventually.