Is prison population growth slowing down?

As detailed here, earlier this year The Pew Charitable Trusts released a big report entitled forecasting that prison populations will continue to grow sharply over the next few years.  However, this new Washington Post article suggests that prison growth has slowed considerably this decade.  The article, entitled "Influx of U.S. Inmates Slowing, Census Says: Number Incarcerated Still a Record High; Sentencing in '90s Cited as Factor," starts this way:

After two decades of massive growth, the U.S. prison population began to level off in the first six years of this century, according to 2006 census statistics released today. At nearly 2.1 million, the number of adults in correctional institutions remains at an all-time high. Still, that figure represents a 4 percent rise since 2000 -- nowhere near the 77 percent spike in the prison population from 1990 to 2000.