A rather long time ago, I had asked how to track changes in Emacs/LaTeX, along the lines of what Word can do. There were many suggestions at the time, along the lines of using CVS, and one person had even mentioned 'texdiff'.
I actually got around to trying latexdiff today, and it actually works quite well. Given an old and new LaTeX document, it will output a "diff" TeX file that when compiled marks changes in coded colors; blue for insertions, red for deletions. People I know use this all the time for managing changes with collaborators.
The program itself can be run as a standalone Perl script, so it's quite portable. I plan to use it more often.