As to the second phenomenon, it seems that while outside a monetary union deep current account deficits worry investors and can, in extreme situations, lead to currency crises, for countries that have already joined the common currency they do not matter much. An example of the three Baltic States (Estonia, Latvia and Lithuania), whose currency board arrangements are close equivalents of a monetary union, shows that enormous current account deficits (9-16% of GDP in 2006) have no apparent negative consequences for the economy. The case is, however, different with inflation pressure. In theory the margin for local demand-driven price increases in small member states of monetary unions is very narrow. This is guaranteed by the so called law of one price – the expectation that the same product should have the same price in various countries of a monetary union. In practice, however, there are several obstacles for this law to hold perfectly – some goods cannot be traded, most goods do not have perfect substitutes, there are transportation costs and tax differentials – so local demand pressures can play a role in driving prices in monetary union member states. As a consequence, products manufactured in these countries become more expensive and such countries loose competitiveness (e.g. Estrada, Lopez-Salido 2001). It is relatively difficult to foresee how the Polish economy will react to demand pressures once in the euro area. However, as in the case of asymmetric shocks, labor market flexibility is probably the best answer to the described phenomena.
However, the estimated scale seems to be much exaggerated. One problematic issue is related to the  BIS Review 6/2007  1  fact that before the eurozone, we did not have examples of currency unions between developed countries. So the Rose study was based on data on currency unions involving poor and/ or small countries. As noted by Micco, Stein and Ordonez (2003), “one does not need to be a eurosceptic to wonder whether such findings are directly applicable to Europe’s single currency”. Follow-up studies (e.g. Rose and Wincoop (2001), Kenen (2002), Persson (2001)) attempted to correct the Rose estimates but arrived, rather inconclusively, at anything between a 50% and 150% growth of bilateral trade. Recently, the first studies based on euro area data emerged. These show that the trade creation effect of the euro was substantial, although (until now) by an order of magnitude smaller that the original Rose estimate (e.g. Micco, Stein and Ordonez (2003)). Our knowledge about trade creation effects of the euro is still far from complete and we will probably have to wait another 10+ years to have enough data to draw firm conclusions about its magnitude in the eurozone. Now let me move to the cost side. As already noted in contrast to the benefits, some costs have a contingent character. They are tail-events – rather unlikely but with a possibly high impact if they happen. Let me concentrate on two issues: -  asymmetric shocks,  -  arising micro- and macroeconomic imbalances.