I'm not sure if this is the preferred technique or not, but it's something I use for very tight downhill switchbacks.
...and that is to take your inbound foot (right foot if turning right) off the pedal and and hang your leg out and back. This helps keep the weight on the inside of the turn, without leaning the bike and risking a washout.
I've found this technique allows me to move faster through the switchback, and with *much* more control. I'm sure there are times it wouldn't work, like if you had to pedal over something right after the apex of the turn.
A modification of this (which you may recognize from road riding) is to simply lean your inside knee out in the direction of the turn. This accomplishes the same thing.