How do I show 'in-application' differences?
Currently besides the Import patches sheet, differences are not show inside MacHg itself.
However, in the history view if you double click on a specific changeset all the files in the changeset will be displayed in your diffing program. Normally diffing programs are quite fast and can prepare several file diffs a second. So opening something like 30 diffs might take say 10 seconds. Now stepping through those 30 files might take a minute or two as you inspect each diff in its surrounding context and you don't have to concentrate on trying to disambiguate the [unifed diffs]. Its much faster than trying to look at these changes in a unified diff...
If you have a range of changesets selected in MacHg double clicking on any selected changeset will bring up the the diffs for all the files in all the selected changesets.
Of possible interest is my commentary about unified diffs and gui clients.
My plan is in the medium future to add a "[Flat File View]" and along with that I will likely add some "in-application" diffing capability in some form.