To be honest, I don't know the exact definition of M3 or how meaningful it is as a statistic. I'm just countering some replies that said the Fed is hiding this data because it doesn't look good. The Fed's decision may well be based on legitimate issues with distortions in the data used to calculated M3 or the economic significance of M3. If the Fed thinks the data has distortions that are making M3 growth look higher than it is, then it would make sense to stop publishing M3 beacuse the distorted data could increase inflationary expectations, and that would be damaging to the economy. But I really don't know why the Fed stopped publishing this data. We'll have to send an email to Bernanke and ask him.
My point is just that this decision may not be the deep, dark government conspiracy that some think it is.