\ref and \pageref in ways that make
\setcounter{foo}{\ref{bar}}
(etc.) not work; thus the technique may not be relied upon.
The solution is to use the refcount package (incidentally,
by the author of hyperref). The package provides four
commands, all similar to:
\usepackage{refcount}
...
\label{bar}
...
\setcounterref{foo}{bar}
(the other three are \addtocounterref, \setcounterpageref
and \addtocounterpageref).
The package also provides a command
\getrefnumber{label-name} that may be used where a
‘number’ value is needed. For example:
... \footnote{foo bar ...\label{foofoot}}
...
\footnotemark[\getrefnumber{foofoot}]
which gives you a second footnote mark reference the the footnote.
(There is also a command \getpagerefnumber, of course).
The commands could be used by one determined not to use
changepage to determine whether
the current page is odd, but it’s probably no more
trouble to use the fully-developed tool in this case.
This answer was added: 2011-09-08
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=labelcount