25% of British Twitter users have purchased something directly as a result of a Tweet

"Bruce Daisley offered some impressive Twitter user statistics from UK:
80 percent use Twitter on a mobile device
70 percent use Twitter out and about (not at home)
25 percent purchased something directly as a result of a tweet.
More than 50 percent say Twitter gives them the latest news, faster than other sources.
This means, said Daisley, "if an alien ever lands on earth, over half the Twitter user base says they'll see it on Twitter before hearing about it elsewhere." This makes Twitter content a platform for live content discovery, which is effective not only for relaying news, but also for brands to get out their messages.
[...]
Daisley finished with more statistics showing that Twitter is working for brands:
94 percent of tweeters shop on their mobile phones.
Twitter users engage. Specifically:
70 percent of them research on Twitter.
17 percent use store locators.
7 percent actually purchase.
56 percent of Twitter mobile users say they are influenced by content on Twitter when buying.
37 percent use Twitter before and/or after shopping on mobile.
1 in 3 users say that Twitter has a direct influence on their purchase decision."
Source:  Twitter UK MD Bruce Daisley, Speaking at SES London, quoted by SearchEngineWatch, 11th February 2014
Note - more of the UK stats here