Billionaire investor Warren Buffett has a message for wealthy Americans: Give away your money. Last June Buffett announced he was donating 85 percent of his $44 billion fortune, most of it earmarked for a charitable foundation established by Microsoft co-founder Bill Gates and his wife, Melinda. Although Americans donated more than $7 billion for hurricane, tsunami and earthquake relief in 2005, the super-rich, in general, have not stepped up their donations to match the economy's growth. Some in the philanthropy community argue, in fact, that Americans' self-image as uniquely generous is overblown. Meanwhile, the foundations that are a mainstay of U.S. philanthropy need more public oversight, critics say. And some scholars question whether charitable organizations are funding medical and other services that the government should provide.