I find Xmarks absolutely essential given the different browsers on various computers I use. However lately I've noticed it wreaks havoc if you use it with browsers that do their own syncing as well.
Case in point: Chrome Sync and Windows 8's own syncing for Internet Explorer 10. Chrome occasionally creates duplicate bookmark folders, or splits one original bookmark folder into two. With IE10 on Windows 8, bookmarks get duplicated at the root level with names like "Some site__1" and "This awesome site__2".
Just wondering if fellow Xmarks users notice the same behaviour? For now things work if I disable bookmark syncing in the respective browsers.