UK Internet visits to www.twitter.com have increased by 631% over the last 12 months, with 485% of that growth coming this year. Twitter is more popular with Brits than Americans: last week the site’s share of UK Internet visits was 70% higher its share of visits in America.

Twitter’s size is notoriously difficult to measure, as there are so many access points (mobile phones in particular), so if anything our measurement of internet visits under-estimates platform’s popularity. In her post Heather Hopkins argues that Twitter cannot yet be considered mainstream in the USA, but in the UK it’s getting there. Last week Twitter entered our rankings of the top 50 Social Networking and Forums websites for the first time, and the demographics are also pointing towards more wide-spread adoption. Overr the last 4 weeks, visitors were split 50/50 male/female, while only 15% were from London. 25-34 year olds are still the most over represented age group visiting the site, but 37% of visitors to the site are now 45 and over.

Looking at the Experian Mosaic lifestyle data for Twitter over the same period also paints an interesting picture. The two most over represented types are still both typical early adopters: City Adventurers (High-salaried, twenty-something singles in smart flats in inner urban areas) and Town Gown Transition (Students and academics mix with young professionals in terraces relatively close to universities). However, there are a number of other over-represented types that would imply a more mainstream appeal, in particular Settled Minorities (Young families and singles of varied ethnic decent, in high density, pleasant urban terraces) and White Van Culture (Younger owners, many in good quality ex-council properties, take advantage of local economic opportunities).

Another sign of maturity is that mainstream media organizations are starting to pick up traffic from Twitter. For example, BBC News accounts for 1.46% of the site’s upstream traffic but 1.73% of its downstream traffic - i.e. the Beeb is receiving more traffic from Twitter than it sends there. Other BBC properties in Twitter’s top 20 downstream sites include BBC Sport (1.34%) and the BBC Homepage (0.71%). The BBC Sport feed is very popular: over the last 4 weeks ‘bbc sport’ was the second most popular search term sending traffic to Twitter. As the table below illustrates, it accounted for 5.92% of search traffic to the site, and was joined in the top 10 by two other BBC-related search terms, ‘bbc news’ and ‘bbcsport’.

The other interesting thing that the table above highlights is the growing tail of people search terms sending traffic to Twitter, something that we’ve highlighted before with regards to another social network, Linkedin. This most recent top 10 includes Kevin Rose (founder of Digg, drinker of tea), the blogger Los Havros, and Molly Wood (executive editor of CNET’s Buzz Report).

Microsoft will announce today that they have acquired San Francisco based semantic search engine Powerset. The acquisition price is not being disclosed, but our understanding from sources close to the deal is that the previously rumored $100 million is “roughly accurate.”

The company had raised $12.5 million in venture financing, plus another $8 million or so in convertible debt as bridge financing. That means investors will get a decent return (but not a home run), and the founders and employees will also take some real money off the table.

Google expects to launch new products for its YouTube web video service in the next few months and sees reason for closer cooperation with Yahoo, Google chief executive Eric Schmidt said on Thursday.

Schmidt has said getting the video sharing site to make money is the web search company’s top priority for the year. He did not give details of the products, however, and they are not even in initial, or beta, testing.

At the company’s annual shareholder meeting, Google co- founder Sergey Brin said YouTube and DoubleClick, an online advertising company bought by Google earlier this year for $3.1bn (?1.55bn), are still small businesses compared with its core search and advertising business.

"They both have potential, but for it to be a sizable part of our revenue, you’re going to have to wait at least a couple of years," said Brin in response to a question about when those acquisitions would make a significant contribution to the company’s bottom line.

Google bought YouTube for $1.6bn in 2006.

The web search leader played a large role in the takeover battle between Microsoft and Yahoo. During a two-week test, it sold search advertisements on rival Yahoo last month as part of Yahoo’s attempt to find an alternative option to Microsoft’s offer.

Schmidt said the trial run provided good reason for the companies to discuss cooperation, but there was no deal yet.

"We view the test as successful," he told reporters before the web company’s annual meeting. "That’s a good basis to talk to Yahoo some more."

The Google CEO, speaking later at the shareholder meeting, said the company will continue to growth faster outside of its home market. Google generated 51% of its revenue outside the United States in the March quarter, but Schmidt said he expects that figure to grow over time.

Without giving a specific time frame, Schmidt said he expects 65% of Google’s revenue to come from abroad. Eventually, non-US revenue could be even higher.

Google co-founders Brin and Larry Page also fielded a request from one shareholder who asked the pair not to split the company’s stock, which closed at $583 on the Nasdaq.

"I think that’s the first time we’ve had that request," Page said with a chuckle.

Brin played the straight man: "We have had no problem honoring that thus far and I don’t expect that anything will change in that respect."