Apparently, the currency in circulation has been soaring. One would think that the trend should be reverse due to credit cards, debit cards, online peer-to-peer payment systems, etc. Paul Krugman suggests
the reason for this boom in paper currency is the low interest rates. According to Krugman, the "opportunity cost of holding cash has gone way down." This WaPo article
makes the case that Krugman is wrong, and the main reason for the boom is inflation fears in other countries.
These articles had me wondering. Are you holding more cash in your home due to the low interest rates? Even if interest rates were zero, I would still hold the vast majorit of it in a checking or savings account for reasons of safety.