And you thought it was mostly Americans addicted to the SMS/IM/web presence thingamy… ? Web measurer Hitwise says it's the reverse - at least, proportionally . "Last week the site's share of UK internet visits was 70 percent higher its share of visits in America," said analyst Robin Goad. " Twitter cannot yet be considered mainstream in the USA, but in the UK it's getting there ." Its growth here - 485 percent so far this year and 631 percent year-on-year - is slower than the eightfold annual international increase , though. Twitter may seem too esoteric and the crowd too geeky to be adopted by the Facebook masses, but Goad says the "demographics are also pointing towards more wide-spread adoption". Last month, the audience was evenly split on gender and over-45s made up 37 percent of users. And, while the most prevalent users are high-rolling "city adventures", students and young professionals, young families, ethnic-minority singles and "white van culture " (for our American readers, "a white van man" is sort of equivalent to a pick-up driving worker) are also heavily represented, suggesting "more mainstream appeal" , Goad said. Fancy metrics aside, the barometer I always use is the girlfriend test - if she's adopted a new technology (hey, it happened with Facebook and Last.fm), you know it's reached a tipping point; she started tweeting several weeks ago. Now if only Ev and Biz would tell us their business model.. Related Twitter Buys Micro-Blogging Search Site Summize; Reportedly $15M Cash+Stock