Avoiding overtraining is far better than recovering from it.
I think that most people when they are new to training overtrain.
This applies to both weights and cardio, there is too much of a good thing.
Really, I don't think that it is necessary to train more than 5 days a week. For those of you who are trying to 'tone up' (which really is putting on a bit of muscle), less is more. I would recommend only training 3-4 times a week, and have planned weeks off, or weeks where you download or lift lighter, just mess around in the gym when you are working out a new routine, get the feel of the movement or machine.
Cardio, vary the intensity.
Have a few other forms of exercise that are really different but fun for you time out of the gym, dancing, Hatha yoga, rock climbing, hiking, riding a bike.
I think the longer you train, the more in tune you get with your body.
I have had this week off, actually I think it will end up being about ten days by the time I get back to the gym, and I can feel my energy and enthusiasm for training coming back to full intensity.
I would also recommend having planned diet breaks, so a cheat meal or cheat day once a week, a whole week off, or if you still want to eat really clean, just make sure you get in more calories at least once a week.