\def\RCS$#1: #2 ${\expandafter\def\csname RCS#1\endcsname{#2}}
\RCS$Revision: 1.3 $ % or any RCS keyword
\RCS$Date: 2009/10/06 22:23:45 $
...
\date{Revision \RCSRevision, \RCSDate}
If you’ve entered the brave new world of Subversion, the package svn may be for you. It has explicit cleverness about dealing with dates:
\documentclass{<foo>}
...
\usepackage{svn}
\SVNdate$Date$
\author{...}
\title{...}
...
\begin{document}
\maketitle
...
\end{document}
will (once subversion has committed a copy of the document)
cause \maketitle use the date that has been written into the
$Date$ keyword.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=RCS