I am becoming a great fan of subversion. Having used some version of it when I did a couple of internships in undergrad days, I did not feel a great need for it during my PhD projects. However, I am now convinced that life may have been much more efficient and organized if I had used it. This includes cases when I was collaborating with three co-authors or reverting to a previous version of my paper.
Those of you who are unfamiliar with Subversion, it is a version control software which helps maintain the latest and previous versions of the source files These source files could be for one of the most commonly used programming languages or the Latex typesetting software. Importantly, Subversion is an open source program, which is freely available and always undergoing improvement.
Not only is subversion a great tool to have backups of your current project but also an easy to use tool for synchronizing changes by collaborators. This enables avoiding conflicts in the document and an easy way to keep track of who is making what changes. It also increases the possibility of researchers in your group collaborating. If you are not too comfortable with command line, there are front end programs for subversions. One front end program which is especially useful (for Apple computers) is TextMate. The documentation for subversion is available from here. The associated book provided in-depth details of information regarding Subversion. However, it may be better to consult it for specific issues rather than leisure reading!