Last year was another good year for millionaires  though their pace of growth is slowing.

According to a new report by Boston Consulting Group out today, the number of millionaire households in the world grew by 12.2% in 2010, to 12.5 million. (BCG defines millionaires as those with $1 million or more in investible assets, excluding homes, luxury goods and ownership in ones own company).

The...