In 1970, the U.S. Supreme Court banned imprisonment for unpaid criminal court fines that the debtor couldn't afford to pay. But, the practice is nonetheless alive and well in 2009.
On the merits, the trouble is, that the fines are often small, and the cost of incarceration is great. So, it never makes the state better off financially in cases where there is a true inability to pay. There may be some strategic value to using the remedy for collecting debt (which used to be called "body execution" and is now called "civil contempt" in domestic relations cases where the remedy is used more frequently but with more attention to the ability to pay limitation on the lawful use of the remedy), primarily as a threat, in cases of mere reluctance to pay. But, inability to pay is very often real, and incarceration undermines collection from people whose primary asset is their ability to earn income.
Absent the intervention of third parties like the ACLU, people who can't afford to pay court fines, also can't afford to litigate issues like this one and force compliance with clearly established constitutional law.
Equally notable is the way that this illustrates the impotence of the U.S. Supreme Court. There are simply too many issues swirling in the lower courts, and too many courts that report to no one but the U.S. Supreme Court (more than five dozen), to which it may only react in a piecemeal fashion for the U.S. Supreme Court to impose its mandates upon the judicial system. The U.S. Supreme Court provides definitive guidance which the lower courts can take if they are inclined to do so. And, usually, lower courts do follow its lead because they are supposed to do so. But, there are real limits to the practical ability of the nation's highest court to insist upon the supremacy to which it is theoretically entitled.