I havent heard of any problems with sludging. I dont think anyone will have sludging probs as long as the oil gets changed like its supposed to.
I run Mobil 1 in my Pfinder, I have since I bought it at 16,000 miles. I havent removed the valve cover but I do look down inside when I take the oil cap off... It looks good and clean in there. I can still see the color of the metal. Love it!