Here's what I've come up with as far as use cases for bookmarks. Feel free to add to this, or comment on the ones already here; should all of these be possible, or are some unnecessary?

• global, most recent bookmarks - when restoring, should restore whatever playlist they were on, even with the database
• single-file-based saving and restoration - user would save before they stopped playing a file (or auto-save), then when they want to restore the bookmark they'd renavigate to any playlist containing the file, select the file, and load the bookmark from there (auto-reload bookmarks comes into play here)