http://www.bodybuilding.com/fun/matt13.htm
quick link for some info
anyway..basically there are studies out there that show you burn more fat doing cardio in the morning b/c you are basically coming off of a fast of say 6-8 hours and you most likely have no carbs/sugar left to burn and you would be getting your energy from stored fat
some people say they like this way, some don't
some will argue that it takes away from intensity b/c you have no "fuel" in your system, and also that you have a greater chance of losing muslce that way
personally when I want to burn more fat through cardio, I don't eat for about 3 hrs prior to training...I get my heart rate up on the treadmill or something for about 5 minutes, then make sure I keep a good pace when doing my lifting, checking my HR periodically to make sure its in a good fat burning range..then I will follow my lifting with additional cardio, mixing HIT style and light-moderate lengthy sessions of about 45 minutes...slow jog or walking..mostly walking cause i hate cardio..lol
anyway..I say to each is own man...if morning cardio works for you then do it...if you notice you are losing muscle by doing it in the morning..either stop..reduce ..or supplement with something that is anti-catabolic
overall I think you will burn more fat in the morning, however with everything there is a sacrifice, and in this case could be muscle and/or decrease in intensity when hitting the weights.
h19