I, too, have the 3.0, and I have had no major issues with my car -- at least not problems isolated to the 3.0. The very few (minor) issues I have had are issues that plague the X5 across the board (window regulator, power mirrors suddenly going haywire). I have been very, very pleased with the car, and have no major complaints at all.
As far as power: The 235hp is misleading. On paper, you'd think it is under-powered considering the weight of the vehicle. All I've got to say is: drive one. BMW has done a marvelous job with the gearing, and the car simply is NOT under-powered! Is it as fast as the V8? Of course not! But, very, very rarely have I wished for more power.
You'll fall in love with the car, trust me.
Juan