To run latexdiff on a CSL machine:

/s/texlive-2010/bin/latexdiff --flatten [flags] old.tex new.tex > output.tex
(--flatten is suggested, not mandatory; see below.) Then run Latex on output.tex and fix any errors (more on that in a bit). On other machines, if latex is in your path, latexdiff might be there and available as well. Try it and see.

If you get errors and don't see why immediately (or you see lots of ^Ms in the output when you open it in Emacs, run dos2unix blah.tex on the input files and rerun latexdiff. Make sure you get any files that are included. See below for more on this and other possible errors.

You need both versions checked out at once, which means you probably need to copy your working directory to somewhere else (or else check out a new copy), then revert it to an older revision (with svn up -rold).

By default, latexdiff does not follow \input or \include commands. The --flatten flag instructs it to. There are a couple limitations:

The output may not be legal Latex. Here are some problems I've run into:

Finally, I've also messed around with the formatting of the outputted file. In particular, I've softened the colors used in \DIFaddtex and \DIFdeltex, though I'm not sure what I used. I think it makes it a bit easier to read.