As of July 2014, US citizens will be taxed on their worldwide income, even if they live and work entirely abroad. The affects dual citizens particularly hard.

http://en.wikipedia.org/wiki/Foreign_Account_Tax_Compliance_Act#Controversy

http://www.huffingtonpost.com/wendy-n-powell/expatriate-tax-sense-or-b_b_5716039.html
http://blogs.wsj.com/washwire/2012/05/18/tax-history-why-u-s-pursues-citizens-overseas/
http://www.cbc.ca/news/politics/canadian-banks-to-be-compelled-to-share-clients-info-with-u-s-1.2437975
http://www.cbc.ca/news/canada/u-s-fatca-tax-law-catches-unsuspecting-canadians-in-its-crosshairs-1.2493864
http://world.time.com/2013/01/31/mister-taxman-why-some-americans-working-abroad-are-ditching-their-citizenships/#ixzz2qQrfCb00
http://www.theguardian.com/money/2014/sep/24/americans-chased-by-irs-give-up-citizenship-after-being-forced-out-of-bank-accounts
http://isaacbrocksociety.ca/2014/09/15/democrats-abroad-publishes-fatca-research-fatca-affecting-everyday-americans-every-day/

http://globalnews.ca/news/1072303/over-3100-americans-renounced-citizenship-last-year-fbi/