The book class (and its friends and relations) automatically changes the display of page numbers in the frontmatter of the document to lower-case roman. This is fine for human readers, but it confuses hyperref since there are pages which seem (to hyperref) to have the same page number. Fortunately, there are configuration options to make hyperref "do the right thing".
The two options in question are:
plainpages=falsetrue' - the default -
hyperref writes page anchors as the arabic form of the
absolute page number, rather than the formatted form.)
pdfpagelabels\thepage to the PDF file so that
Acrobat Reader can display the page number as (say) 'ii (4
of 40)' rather than simply '4 of 40'.
..n'; they may be used independently, but usually are not.
The recipe isn't perfect: it relies on \thepage being different
for every page in the document. A common problem arises when there is
an unnumbered title page, after which page numbers are reset: the
PDFTeX warning of "duplicate destinations"
will happen in this case, regardless of the options.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=pdfpagelabels