Night Skiing, Weekdays, most people avoid black diamonds
Weekends, Crowds, elevation, Boorish classless people
Mountain High has some good quality runs and is a great place to ski/board at night or on weekdays. Of course, it's icy, but during the week (and nighttime), there is hardly anyone there. It's cheap, too!
Lines can get long on the weekends, and there are beginner level snowboarders careening out of control all over the place. Many of the runs are not very wide and the people who just buzz around out of control with not a clue in their heads make it dangerous for families and those looking for a casual time, especially on weekends. Go on the weekend and WATCH OUT!
Weekdays and night skiing on the other hand are superb. There are better resorts in SoCal, and because of its proximity to LA, San Bernardino, and the rest of SoCal, it seems to draw a much larger share of idiots, cretins and the mindless hoi polloi.