I'm interested in the brake light function. How does that work? Some sort of microswitch mounted somewhere near one (or both) brake levers?

Sorry, I think my explanation was vague. I can choose between high and low when I turn it on, it's not connected to the brake levers. I've thought about doing that, but I prefer being able to just leave it on high during the day.

I think i mainly depends on where you ride. If you ride in the city with a lot of flashing lights more is probably better. I mostly ride at night on pitch black country roads so I use a Super Flash Turbo and a Knog strapped to the back of my helmet and I have yet to have a problem. Knock on wood.

We need a chart that plots number of tail lights on one axis, and risk of being hit on the other axis, derived from real world observations. At some point the drop in risk as light numbers increase would taper off, and that would tell us how many to use. I really doubt I can find that data. As a driver I can say that even one red blinky on the rear, if it's a half way bright one like a planet bike superflash or one of the good Portland Design Works lights like I have, is visible for a very long distance in the day time, even when I'm heading into the morning sun.

We need to be careful though that we use one less than what would prompt people to call us paranoid.

I posted earlier that I have four lights in the rear, but after some observation and thought, I don't think that many is really necessary.

I say two decent lights is all you really need. I say two because of the "redundancy by design" concept. You could have one uber light, but if it fails, then what?

I'm going to move the 4D Toplight from the seat post back to the rack (where it was designed to be) and the NR Cherrybomb will either be on the seat post (currently just under the wedge pack) or the helmet, depending on what and where cargo is on the rack.

As for flashing lights in general, here in NYC the new Citibikes have flashing front and rear lights, and these are sanctioned by the city. I guess if they're illegal the city doesn't know it.

For brake lights, my MagnicLight has that function due to the fact that it is mounted on the brake arm, and draws power from the rotating rim. As you apply the brakes the light is closer to the rim and draws more power. I'll have to admit though it doesn't work too well the way I have it mounted, but I'm sure I could make it work better.

Many years ago I had a crappy rear light that used a micro-switch on the rear cable somehow.

There are some dynamo lights that work by sensing the frequency (basically the number of pulses generated as the magnets pass) and a micro controller to tell the rear light to get brighter when the frequency drops.

There are or were a couple of accelerometer based services too.