I have used this service for quite a while, so I’m pretty disappointed that it is being discontinued. Formally called Foxmarks, Xmarks was a free browser sync service that allowed you to sync bookmarks and passwords across browsers even on different platforms.
Xmarks will discontinue the service in January, and they are giving the option to delete all your data now if you wish. I have removed all my data and uninstalled the browser extensions. Now I will just rely on Firefox sync and MobileMe.
http://www.xmarks.com/about/shutdown