I run 2-3x/week and weight train 2-3x/week... I work my legs only once/week, and do a body split of back/biceps and chest/triceps on the other two days, with some abs/shoulders thrown in there time permitting...
It's a very good idea to work your legs. A few years ago I saw a doctor and mentionned to him that I was running, he was surprised that I didn't have sore knees "For a woman my age"

... Another time I visited him he noticed that I was muscular and asked if I weight trained, I said yes, and he said "So that's why a woman your age doesn't have sore knees, your knees are only as strong as your ligaments and muscles are." So I guess if you have strong muscles and ligaments your bones and joints will be strong

... So, in my eyes, weight training is all good