billion tweets were sent in 2010, according to Twitter. It's hard to imagine what the cumulative impact of all that keyboard tapping -- whether inane or enlightened -- may be. Earlier in the week, Twitter summed up what it considered the "10 Most Powerful Tweets of 2010" -- a slightly less quantifiable quality than raw popularity. Some of these were predictably political: the White House welcoming Russian President Medvedev to Twitter, the Prince of Wales' private office announcing Prince William's engagement to Kate Middleton.