I'm tempted to try one out. Maybe add a rectifier to a small battery (or large capacitor), use a more modern blinking LED rear light, and perhaps swap the headlight bulb to a replacement LED. I like the generator idea (no batteries), and I probably wouldn't be going faster than 15mph at night anyhow.
I assume the overvoltage protection on these systems is built into the generator, right? Is it easy enough to defeat? I'd rather modify the wiring at the bulb and/or insert appriopriate circuitry, so that in over-voltage situations, I could charge a battery or run a second light (maybe the second light comes on above a certain speed). I have an electronics background, btw, just not a background in bikes or bike generators. [I like the idea of the hub generators but a) don't like the price and b) don't like the idea of building wheels just yet.]