I happened to look at my fronts today, before reading this, and noticed mine are showing signs of scuffing wear but they will probably rot off before wearing too smooth. 1-1/2 year old and not quite to second engine oil change yet. Fronts will wear faster than rears even on 2 wheel drives just because of wear when sterring, but the amount of time spent in 4wd will add to it. Fronts rotate faster than the rears, so amount of time 4wd drive is engaged will affect the wear. I don't worry about it though, I am always in 4wd but have no reason to run on the road.
If and when the time comes to replace the fronts, like Catdazer mentioned I will probably look for some R4s that are close to same circumfrence as the R1s I have. Love the R1 on back but a little wider tire up front would be nice.