Allowing your wheels to spin for extended periods of time with clearance between the tire and anything to hold on to is a :nono:

Not good for your alignment or a tranny (well worse if it would have been an automatic).

The way I always get out of snow is to rock the car, longer you let your wheels just spin the more heat and what your stuck on will turn to ice rather than moveable snow. Also like Shingo said, start out in 2nd gear, with real low RPM's.