It is interesting you bring this up as it came up in the clinic today. The etiquette is to allow a faster rider past when it is safe. You don't have to get off your bike and pull right off the trail, but if there is room to pass, you have to give the faster line to the passing rider.

This weekend in Temecula there will be lapping, and the singletrack at the end of the loop is tight. I would suggest slowing to allow pros to go past as it will be stressful along the ridge to have someone breathing down your neck.

Having said that, if it is someone in your category, if you have worked hard to beat them to the top, you don't have to let them past on the downhill.

Good luck!