I moved my 2 headlights down to the fork today cause they get in the way up on the handlebars. I haven't had a chance to try em out in the dark yet. Does anyone else do this - or is there a reason I shouldn't keep them down there.

If they get turned into the spokes, it will mess up the light and most likely the spokes.

I keep a knog bull frog blinky light on my fork. The only thing I've notice so far is that it collects any sand/dirt/grime falling from the fenders. In your case it may make the lens dirty and block some light. But it's easy to wipe down if it does get dirty.

I've been wondering this myself, but have yet to try it.

I suspect you're going to have a dark spot right up the middle due to the rim itself being in the path of both lights. I'd have something up higher in addition to shine a beam in front of the wheel so you don't catch unseen holes/items in your path.

Passed a guy the other night with fork mounted lights. He also had either a bar light to fill in, or a helmet mounted light. He was approacing an intersection to my left and I crossed before he got there, but I was cool to see the two lights down low. Really seemed to light up the road well.

This works well with two lights. Yes you get two rim shadows but they are not significant.
Lots of long distance riders run them there as it saves room on the bars for comfy hand positions and handlebar bags. I used to use two cateye el530s, one on each side.
Drawbacks: You get somewhat better visibility to others if your lights are higher, and also you can see better over bumps with a bar mounted light.

Mounting the lights low makes them more effective because the vertical separation between the lights and your eyes brings emphasizes the texture of the road and makes it easier to spot debris and potholes. This mounting is very popular among randonneurs who ride many hours at night.

The location will cause shadows from the tire that go off to each side, but using two lights will fill those shadows. Even so, it's a minor annoyance that you quickly get used to.

Just be sure that your mounting to the fork is secure.

I think this arrangement is more interesting to look at than to see with. I have tried it with dual generator lights, and the arrangement can be a bit of a pain, especially if you want to turn on a secondary light while riding. I ended up moving my lights closer to the cockpit, on a modified bar outrigger for a computer. (Also, if you have cantilever brakes, there are considerations of interference with the lamp housing and the brake arms and straddle wires. If you have a front rack with braze-ons, you can buy hangers that let you place the lamp toward the forward edge of the rack underside, below the bag bottom and out of the way of the fork. This still doesn't get you around the switching inconvenience, but it looks good and works better than a fork mount, IMO.)

The idea of illuminating rough spots better by having the beam closer to the pavement does not result in enough benefit to outweigh the inconvenience of having the switches out of easy reach.

Switches do not necessarily have to be located on the lights. I currently have a remote handlebar switch for the lights on my 20" wheel folding touring bike (single headlight at fork crown level and taillight on rear fender), but the even better way is to use a hub generator setup with LED lights, which has such low drag and long life that it's just not worth the bother of ever switching them off.

You want the lights at car headlight level, that is if you're more interested in maximizing your visibility to cars.

When using dual generator lights, having the secondary light mounted a little higher has merit so that you can more easily reach the switch. This is most important with halogen generator lights, such as the Schmidt E6 since you get more light from a single E6 climbing steep hills at speeds below 10-11 mph. I know some randonneurs who mount their primary light on the fork blade and the secondary at the fork crown for this reason.

I disagree with trading off light effectiveness for switch convenience. Most bike lights are marginal at best. The lights shown in the OPs post are much more effective when mounted in the position shown. I had similar lights for my first season of randonneuring and was very pleased with their performance when mounted on the fork blades.

With battery lights, there is little reason to turn one light on and off while riding unless there is a need to conserve batteries. However, in such case, a better strategy would be to carry a spare set of batteries so you can run both lights all the time.

And maximizing your chances of being recognized and respected as a vehicle on the road. That would be around fork crown level on most bikes. That's also why I prefer larger headlights. And one of the reasons I dislike helmet mounted lights, especially when they are the only front light.