Reading the discussion about having two different power sources, has anyone developed a dynamo lighting system that simply charges a battery or capacitor that powers a light? A system like that seems like it would solve the problem identified by cyccommute (the light cuts out when the bike stops). It seems like it would be very simlar to hybrid cars with regenerative braking (except the charging is during the acceleration, not deceleration, phase).

For the record I'm a commuter that sticks to the roads, and my $120 bike light battery just burnt out after a year. Not that I'm totally against batteries, but I'm not so ecstatic about having to shell out $120 a year for a new battery (plus $200+ for the initial cost of the light at deep discount) when I might be able to pay $200-$250 for a light that will last indefinitely. Maybe I'm just cheap, but that's 12 extra 6-packs of fancy beer I could be drinking.