In addition to just letting the moneys lie in the account you can also buy shares of special* funds, so you can participate in the financial markets, hoping to increase you return on the money saved. This does, of course, carry additional risk, since markets tend to go down sometimes as well. Once again the time horizon should be a factor for this decision.
*- special funds: the upper limits for stock- and foreign currency holdings are regulated and can not be freely chosen. please note: This page was last updated February 2004. Also read the disclaimer.