Thanks to answering yahoos, last night I learned that caffeine promotes adrenaline secretion, which in turn unbinds fatty acids from fat stores. Fatty acids are an energy source, and compete with blood glucose, which doesn't directly reduce insulin secretion, but does decrease insulin sensitivity. Upshot: the body utilizes less available glucose.

Ideally then, assuming you drink coffee before or with breakfast, your morning meal should be low-carb, e.g. bacon/sausage/taylor ham, eggs, and cheese. If you don't utilize some of that chemical energy, it will get re-fixed as stored fat.

From this we can conclude that a dose of caffeine can provide a real chemical energy boost and promote loss of adipose when taken before a moderate workout. Dunno what the effects are on lean tissue and organ systems, so without an expert opinion I'd be leery of working out too hard on low blood glucose, relying only on a caffeine-induced fatty acid rush for energy.