I discovered today that the MacBook powers its USB port even while the system is asleep. I've had systems in the past that I've tried this with and never had any luck.
The MacBook is now the biggest most expensive external battery pack for a cellphone one could ever have! I just charged my iPhone almost all the way, while watching streaming tv on it. This reduced my laptop's charge about 20% (if that).
(don't ask why I wasn't just watching movies on the laptop.. it was a geeky experiment.)
Man, at what point did I become a big old Apple fanboy?