Just recently I have been reviewing several sites and storing the bookmarks as I went, I have been keeping them in a seperate review folder.  I had noticed that XMarks was not running, when I had started it up, it flagged there was a problem with syncing and that it would carry out a download.  While doing this it had not synced my recent bookmarks I had added on the machine, so once it had completed the download I managed to lose my recent bookmarks.