This is just a quick note about a nice emacs feature.
If you develop with emacs, you may have heard of/used ediff. This is a very handy diff program which runs inside emacs. We use this with a custom hook at work to work with our version control system. I found out that it works nicely with more standard version control systems as well.
The main way to use ediff is the command
This lets you choose two buffers to diff. To do this for different revisions of a file you can use the command
This will ask for which file you want to view revisions of (default, the current buffer), and the two revisions to compare (default latest revision and the current state). The you will have the file you asked for loaded in the two revisions you asked for.
Using mercurial personally I find this more informative than the output from hg diff in complicated cases. I believe this works for any version control system recognised by emacs, e.g. mercurial git and subversion.