Low blood glucose levels = bad for weight training. How bad? I don't know. But considering that, like CS mentioned, you can raise blood glucose levels relatively easy, there's not much reason to do it in a true fasted state. Drink 8 oz. of milk and a piece of fruit or a slice of toast or something. Just something to kick the glucose levels back up. You don't have to do a BiggT breakfast.
edit: forgot something else . . . "studies have shown" that amino acids in teh bloodstream before your workout have a large impact on protein synthesis (or something else that's important, LoL, I don't remember the details). You can achieve this by just eating like a normal person, LoL, or by downing a small bit of protein shake 30 min's before you lift. If you eat every few hours, you'll be fine. But coming out of teh nighttime fast, you'll have no/few aminos in the blood. Another argument for drinking a bit of whey and a slice of toast or something beforehadn.