Is there an auto-run key?
You can change the run key from the default "press and hold" to a "push once to toggle" option. For whatever reason, in the time between the demo and the full game, the default was changed from the latter to the former (Needless to say, it was the first thing I changed back).
There doesn't seem to be an "always run" button, so do bear in mind you'll have to re-toggle the run button every time you come to a full stop, or take damage, etc.
Still loads better than holding the button down all the time!