Subversion on a remote server with local copies could be one way of accomplishing this. LyX has good support for SVN built-in and there are many good user interfaces (such as Tortoise SVN for Windows, Rabbit VCS for Linux and Versions for Mac OS X) that make it a point and click affair.
Moreover, you can get free hosting from companies like Beanstalk (http://beanstalkapp.com/). In addition to syncing files, another benefit of version control is that it keeps a log of every change. This can be invaluable if you are working on a complicated project (like a thesis, paper or book). This link has some good information on Version Control in general and Subversion in particular. http://www.oak-tree.us/blog/index.php/science-and-technology/svn Cheers, Rob Oakes
