I kind of have a similar thing. I started riding fixed as crosstraining for running, since I stopped running competitively after college. Now I commute on it, and run errands occassionally, and it's managed to keep me in fairly decent running shape for when I do go back to race. After riding 5-6 days a week for 2 months, with about 3 days of running, I could still drop an 18-minute 5k on a rainy day.