I was working on a project and tried to open it but the progress bar goes to about 95% and then just sits there.
I read through some posts here and verified the XML is valid with XMLWrench and tried to open the autosave files (same result).
I even tried copying _only_ the *.prproj file over to my mac (no media files) and had the same result, with both the original file and the auto saved ones. In other words, it had the exact same behavior on both Windows Vista and OS X and when tested on OS X, the media files weren't there so it seems like corrupt media files are not the cause.
This happens consistently as my projects get bigger, How long did you wait before bailing out? Many people report waits of several minutes or longer. Seems to get worse the more assets you have, and the more complex the timeline.