The Value Of A 2012 Social Media Share Is $3.23 – According to Eventbrite

$3.23 = Dollar Value Per Share—the average value of the additional tickets sold through this share (up from $1.78 in 2010).

Twitter $1.85/share (up from $0.43 in 2010)
Facebook $4.15/share (up from $2.52 in 2010)
LinkedIn $0.92/share (up from $0.90 in 2010)
17 = Visits/share (up from 7 in 2010)

Facebook 14 visits/share (up from 11 in 2010)
Twitter 33 visits/share
LinkedIn 10 visits per share