Good idea to avoid them if you can - they are VERY slippery, especially if you are trying to turn. I recently did a 'cross race with a pavement section that was leaf covered - because of the risk, the promoters actually raked the leaves OFF of all of the corners.

Of course, in the woods, you also have to be very careful of the leaves. Not only are they slippery, but they are hiding the hazards underneath.

That said, as long as you are careful, you can still ride. I'll be out in the woods for a ride tonight.

SheFly