I hit the legs once a week during the season. I just don't train them as intensely as I would during the winter. I do centuries on the weekends, so usually a Tuesday or Wednesday leg workout works best so that I am recovered from the weekend's mileage and I won't be too sore for the upcoming weekend's rides.
I am a much stronger rider when I keep my hamstring strength in balance with the quads. Knock on wood - I have not suffered any injuries or ill performance from muscle imbalances or overtraining yet.....