This works for me too. Working out in the morning (or whenever it is I decide to get up) _always_ gives me more energy for the day and it usually puts me in a good mood too.
I've heard many such articles stating that exercising increases energy levels. However, they never seem to specify exactly what type of exercise.<p>Are they always referring to cardio? I tried exercising in the morning a while back, but I was doing weights. I felt anything BUT energetic for the rest of the day ...