I've just come back to Xmarks after 3 years away. I've deleted all my bookmarks, uploaded a new copy, downloaded manually into other browsers, and all is fine.
However, the Automatic Sync feature of both the Chrome addon (both Windows and Mac) and the Safari extension (Mac only) don't seem to automatically synchronize at all! The addons/extensions notice that there is a change (i.e. I've added or deleted a bookmark) but the change doesn't seem to propagate until I manually synchronize again.
How long does it take for the addons/extensions to force an Automatic Sync?