I added backwards treadmill walking to my gym routine yesterday. Apparently it helps with a whole host of ailments and conditions including lower back pain, bad knees, tight hamstrings, injured ankles and feet. It also improves balance and coordination, and burns significantly more calories than walking forwards.
I must say I felt great after 15 minutes walking backwards on a slight incline, and I'm wondering if it could become socially acceptable outside (providing I wore some kind of mirror attachment).