If Web users' use of "AddThis" is a measure of how people share media – and Ad Age thinks it is – then Facebook accounts for more than half (52%) of our media-sharing, but "Twitter was up 577% this year" overall (13.5% of sharing) and accounted for 52% of media-sharing in Japan, interestingly. Tumblr came in third overall, at 1,299.5% growth (fastest-growing). Google's +1 button has plateaued, Ad … [Read more...] about How/what media we share (by 1 measure)