The popularity of money market funds is owed to their relative simplicity, liquidity and security for investors. Over $2.7 trillion are invested into these types of funds throughout the U.S.
The capability of money market funds to remain stable at a $1.00 net asset value per share (NAV) has been a main draw toward holding these funds. In part of a response to the financial crisis, on May 10, 2011, the Security and Exchange Commission (SEC) discussed allowing the NAV to float above or below $1.00, thereby generating taxable gains and losses on the funds.
A recent survey shows that 77% of corporate money market fund users would move cash out of these funds if the NAV was changed from stable to floating.
Additional data concerning money market funds and their history can be found here.