There are some unnecessary spacing and boxing in the definition of \cleardoublepage. This is a tad shorter:
\makeatletter
\def\cleardoublepage{\clearpage\if@twoside \ifodd\c@page\else
\null\thispagestyle{empty}\newpage\fi\fi}
\makeatother
However, if you know the setup of your document, you can remove many of the conditional statements, since they add a majority of the code. The reason for this is because the command is made to accommodate general document setup rather than be specific to one instance. To that end, if you're typesetting a book that uses the twoside option, you could just as well use
\makeatletter
\def\cleardoublepage{\clearpage\ifodd\c@page\else
\null\thispagestyle{empty}\newpage\fi}
\makeatother
And, if you don't enjoy the @ symbol (which brings with it \makeatletter and \makeatother), you could also use
\def\cleardoublepage{\clearpage\ifodd\value{page}\else
\null\thispagestyle{empty}\newpage\fi}
\usepackage{emptypage}not do what you want? – Lev Bishop Oct 07 '11 at 20:54