I have a problem with using both pdfsync and pdfcomment together: once I use pdfsync, the comment causes a line break, which it shouldn't do. As an example, compile with and without \usepackage{pdfsync}:
\documentclass{article}
\usepackage{pdfcomment}
\usepackage{pdfsync}
\begin{document}
Text Text Text Text Text Text Text Text Text
Text Text Text Text Text Text Text Text Text
\pdfcomment[icon=Note,hspace=0cm,voffset=0cm,hoffset=0cm,width=0cm]{text}
Text Text Text Text Text Text Text Text Text
Text Text Text Text Text Text Text Text Text
\end{document}
pdfsyncpackage should only ever be used for drafts: changes in output are a 'known issue'. Moreover, it is obsolete as SyncTeX is available in both TeX Live and MiKTeX to achieve the same aim at an engine level. – Joseph Wright Oct 01 '12 at 15:41