During the snowmobile chase, Doug is alternately (not) wearing sunglasses.
When Doug is riding in the chair lift with the salesman, there is a man in a yellow jacket riding in the chair behind them. When the lift stops before reaching the drop-off and you see the chair behind Doug, the man is gone.
The first time the outside of the ski resort is shown there is snow on the building as well as on the trees, the ground, and the cars. The snow is gone during the nighttime photo of the resort but reappears the next time the outside of the resort is shown again in the daytime, all in one weekend.