It's crazy, but true! I've been watching Firefly today, and in the episode Safe, River Tam has a flashback to her early life. As I was watching, I thought, "Boy, that actor playing young Simon bears a striking resemblance to Zac Efron. I wonder who does play him, anyway?"
So, I looked it up. Lo, and behold, it is Zac Efron! I've had my mind blowing experience for the day now. I can't find the clip, but you can watch the full episode here, on Hulu.