Xmarks has decided to close up shop because it can’t find a way to make any money. Sad to me because it’s a service I use everyday and is honestly something I’d probably pay for because it works across all browsers on all the systems I care about. Although it is possible to use your own server as an xmarks sync server this is really only a stop gap measure because the plugin is going to need to be continuously updated as new browsers are released. The only answer then is for someone (are you listening Google?) to buy it out or for the team to release it as an open source project.