This problem appeared after I installed XeTeX from TeX Live 2011. Now, many of my files are rendering with a very wide right-hand margin.
Here is some sample code:
\documentclass{octavo}
\usepackage{lipsum}
\begin{document}
\lipsum
\end{document}
When running pdflatex or xelatex on the file, the right 60% of the file is white and the text is all of the right. With xelatex, the output PDF always ignores my custom page dimensions and only gives A4 paper with my text printed very small in the top left corner.