Midwinter I was adding in 3 days a week (about 9 miles total) running. Easy terrain.
It really helped kick start some cardio improvements and weight loss.
I've found that when I focus only on the bike (like the last 2 months) I get sore from hiking and even the shortest run. Running adds impact and builds muscle groups that allow you to move in 3 dimensions (road cycling is a fairly 2d sport, in terms of body mechanics)
Hmm. Guess I need to get back to it... without feeling like I'm getting beat up every week.
Richard - I agree, you are once again master of the obvious.