 I have just over 99,000 miles on my Xterra, and I have already had to replace a cracked exhaust manifold and the supercharger.  Now I am being told that the head gasket is leaking.  I love the styling and capability of the Xterra, but I have been very disappointed by the reliability.  I don't know if the 3.3 liter engine was not properly designed for the stresses associated with the supercharger, but it has definitely not lived up to my expectations.