I've been meaning to try my bike rack on the front, because of your post I did it this morning.
It's a bit high because the receiver is on top of the bumper and you do have to look through the bike while driving, but it's not too bad. And considering it leaves the tailgate free to swing open, or the rear receiver free to tow a trailer, that's not a bad compromise.
Because of the design of my bike carrier, it would be easy to disassemble it, drill a few new holes, and reassemble it to be shorter so the bike isn't as high, I may modify it now so it's ready to be used on the front when I need it. I did the mod digitally in this photo:
Another possible use for the front receiver:
I subscribe to two Land Rover magazines from the UK, I picked up the habit of reading them when I lived in London some years ago and I've kept the subscriptions going - I always find interesting ideas in those magazines that aren't often seen in the US.
For example, I just finished my quick-install front receivers for both my LJ and my JK, and came across this photo in a magazine I was reading the other day. It's a Belgian Minvera (a Land Rover derivation built in Belgium for the Belgian Army), and it's got a front spare carrier.
Then a day later this showed up in Craigslist:
I'm not going to buy the spare carrier that's on CL, but I will keep the idea in the back of my mind in case I ever need to carry an extra spare and I don't have roof on the roof rack or inside the Jeep.