Milton Friedman was not alone in criticizing the UEM, relying on Robert Mundell's theory of OCA (Optimal Currency Areas, 1963). Ironically, in 2009 ,to celebrate the apparent decennial 'success' of the Euro, the European Commission published a book by Lars Jonung and Eoin Drea summarizing " ... approximately 170 publications shows (a) that US academic economists concentrated on the question "Is the EMU a good or bad thing?", usually adopting the paradigm of optimum currency areas as their main analytical vehicle, (b) that they displayed considerable scepticism towards the single currency ... In particular, the traditional optimum currency approach was gradually put into question". You can read it: http://ec.europa.eu/economy_finance/publications/pages/publication_summary16343_en.htm