I prefer workouts that are 50-70 minutes long, and my goal is to workout a minimum of 4 days a week for 50 minutes. I don't always hit it, and sometimes I do more, but my ideal workout week would be 5 days, 50 minutes.
I think more is not necessarily better, especially from a health and injury-prevention standpoint. I've often read that anything over about an hour may be counterproductive, especially with weight training.
Recovery and rest is just as important as working out.