I've continued taking yoga to loosen up my back some more and work on building "core strength".  At the same time, I'm reducing the amount of mileage I run and how I often I run.  I've cut back from about 40 miles a week, running 5 times a week to running 3 times a week and only running 3-4 miles at a time.

The core strength classes are helping a lot in terms of overall physical health.  They're helping me to focus on keeping my abs engaged when I run, which takes pressure off of my back.  Running less makes sure that I stay focused when I run.  When I used to go out for a long run, I must have realxed my stomach muscles and settled into a grove where they didn't have to do any work and the weight of my head and shoulders sat over my lower back.  Now I try to keep better posture when I run and in everyday life and it seems to be helping.

If you're looking for a good core strength building class in Cambridge, MA, Yoga Karma Studios has a good one with Jesse.