This is something I had been wanting to do for quite awhile. Now that I've used them on a few trips it's something I wish I would have done long ago!
First, I'd like to comment on the safety issue that most people bring up, carrying fuel on the outside of your vehicle is a risk no matter where you put it, but if you look at the statistics, a rear end accident is by far the most common and no one seems to have much of an issue with them being on the back. Now I understand that some designs sit higher than others, but plenty of them still sit low enough to get hit. I also don't drive around with full gas cans just for the fun of it. I have always made a habit of filling up my main tank and any extra cans at the last gas station available before heading off road. I also always empty my gas cans into the jeep tank as soon as I have room, to get the weight off the outside and down low into the tank where it belongs. So as far as the gas cans causing my jeep to turn into a fireball, I see no difference in safety between mounting on the sides, and mounting on the rear so I'll take my chances.
Now onto the benefits, I used to have my gas cans on the rear. The weight of two full cans hanging off the back caused quite a difference in handling and made the rear suspension ride horribly, especially since my jeep is usually loaded down with camping gear when I'm off road. Moving the cans up front made a HUGE difference in the ride and was well worth the effort of building the mounts. They don't stick out nearly far enough to cause a problem on 99% of the type of trails I do, but if I was out for a day of rock crawling (rare for me) I obviously wouldn't have the cans on the side. The weight is lower more central and the cans are easier to load and unload when full.
One valid concern that some have, is a rock flying up off the tire and putting a hole in the can. To solve that issue I welded a 1/8" floor into the passenger side. For the drivers side I built a removable floor that flips over to become hi-lift jack base for soft ground. Speaking of removable, if I ever come to a section of tight trees, gnarly rocks or anything else on the trail that I think may hit the cans or cause a problem, it literally takes less than 30 seconds to remove both mounts with the cans still in them (yes, I timed it) and the same amount of time to put them back on on the other side. Mine are mounted in a vertical receiver that is welded onto my sliders, and then held in place by two pinch bolts. They have never even started to come loose and just like Jscherb, I climbed right up on them and bounced up and down to make sure they would hold, not a bit of movement. This is something I should have done a long time ago and for the type of wheeling I do, I see no downside. Keep up the awesome work Jeff, you're an inspiration to people like me to keep building more parts for my jeep!