Mac OS X uses the HFS+ filesystem. Most of the time I don’t think we notice or care what filesystem we use, but in some cases, the filesystem itself is an important feature and even a draw to a platform. The BeOS for example had the Be FileSystem (BFS), which essentially allowed you to tag your files making your files even easier to find. If that sounds a bit like Mac OS X’s Spotlight, then maybe it won’t surprise you to learn that many Be engineers ended up at Apple. 🙂
I’m not an expert on this, but as I understand it there’s the file contents and then various types of information about the file that the filesystem uses. In moving from Mac OS X to Linux, one thing I’ve run into is that some file types, like TextClippings (*.textClipping files) are empty. All the data the file uses is kept in one of those bits of information about the file. Because you’re no longer using HFS+, it is not possible to get the information. In fact, for all I know, it’s actually gone what’s moved to a different filesystem. I think .dfont files also fit in this category.
To my knowledge there’s no way to open the data on a non-HFS system- you’d have to get what you need before jumping to Linux.