As of Version 8.0, MultiPoissonDistribution has been renamed to MultivariatePoissonDistribution and is part of the built-in Mathematica kernel.
As of Version 7.0, NonlinearRegress has been superseded by NonlinearModelFit and is part of the built-in Mathematica kernel.
As of Version 7.0, AdjustedRSquared has become a property of LinearModelFit.
ANOVATable
(Obsolete Regression Common Package Symbol) As of Version 7.0, ANOVATable has become a property of LinearModelFit and NonlinearModelFit.
As of Version 7.0, AsymptoticCorrelationMatrix has become a property of NonlinearModelFit.
As of Version 7.0, AsymptoticCovarianceMatrix has become a property of NonlinearModelFit.
BestFit
(Obsolete Regression Common Package Symbol) As of Version 7.0, BestFit has become a property of LinearModelFit and NonlinearModelFit.
As of Version 7.0, BestFitParameters has become a property of LinearModelFit and NonlinearModelFit.
As of Version 7.0, CatcherMatrix has become a property of LinearModelFit.