i've had both....I run dedicated snows regardless of drivetrain, so my observations are based on snows. i personally would not run all seasons even with awd-- i feel its too much of a compromise. jack of all trades, master of none.
AWD is great for the few days a year with 12+ inches of snow. in 2010/2011, i was able to plow through the massive snow storms we got hit with. but to be honest, by the next day i would have been just fine with RWD. i'm a snowboarder, and would have to say that in the past three years with my X drive, i can only think of two or three occasions where the X drive came into play. and those were when i was stubborn and didnt wait for the plows to knock the snow down to less than a foot.
i personally dont like the raised suspension on the X drive cars-- it makes the car feel "floaty" i also noticed a pretty noticeable drop in fuel econ. my 07 averaged 21mpg with heavy city driving. i'm averaging 17mpg with the same driving pattern.
i plan on getting a RWD F30 this winter. for the vast majority of the year AWD either doesn't come into play, or is actually a hindrance.