I use Mercurial to track changes in my LaTeX documents. While there's latexdiff and the older texdiff to produce a conveniently marked up difference document (like Track Changes in Word or OpenOffice), those depend on having both versions available at the same time -- a bit of a pain when using version control. You have to update to the old version, rename it, update to the new version and then compare them -- far from trivial for documents with many files. Well, now there's a convenient utility to do that for you with Mercurial and Git, scm-latexdiff. Check it out.