Harmonisation
When national laws are harmonised they are made consistent across the EU. Before the Single European Act in 1987, harmonisation of laws required unanimity. Now, most harmonisation rules can be decided by a qualified majority.
The future
The Lisbon Treaty introduces the possibility for a qualified majority to harmonise EU law in sensitive areas. In the most sensitive areas, so-called, 'bridges' or 'passerelles' allow the EU to introduce the use of qualified majority voting if this is agreed upon unanimously by the European Council.
However there are areas like culture and education within the spfere of supporting, coordinating and complementary action by the EU or which Union legal acts may not entail harmonisation of national laws - see e.g. Art. 2.5 and 6 TFU as proposed by the Lisbon Treaty.

