Trail etiquette - riding trails in reverse

All,

If you're going to ride UP a trail which is designed to be ridden DOWN, please try and make sure that there are no more than 2-3 of you as a whole. It's really irritating when you are trying to ride a a trail as it was intended to be ridden, and to enjoy its flow, but are instead forced to stop every 2-3 minutes because 12 people are riding the trail in reverse.

I appreciate that sometimes things are out of your control as maybe there are 3-4 separate groups of 2-3, but really, if the start/end area looks crowded and/or you've seen many bikers around you then one might reasonably assume that there might be others on the trail other than your group.