Mountain Biking

I'm currently researching an article on mountain biking. The effects mtn bikers have on the environment, both positive and negative. Here's an excerpt from the Sierra Club's website concerning effects of mountain biking, ways to reduce negative effects, and trail etiquette.

Effects:

• Significant soil erosion or significant damage to streams or fish habitat.
  Rutting, impairment of trail drainage, breakdown of trail shoulders, and other forms of damage not correctable using U.S. Forest Service trail maintenance standards and techniques.
  Significant disturbance of plants or animals or their habitat.
  Damage to archaeological, scientific, historical, or other significant resources, including rare natural features of interest for scientific study.
  Danger to the safety of bicyclists or other users because of bicycle speed, steep grades, steep terrain, sharp curves, slippery or unstable trail surfaces, or limited visibility. See Appendix D for design features that can improve safety.
  Significant displacement or annoyance of other non-motorized users.
  

Some Methods to Reduce Bicycle Impacts (not in priority order):

• Walk bicycles in certain areas.
  One-way-only trail sections.
  Speed limits (though these may be difficult to enforce).
  Restrict use by time of day, day of week, week of month, month of year.
  Restrict use by season (e.g. to protect soils or sensitive habitats).
  Separate different types of uses at trail heads and congested areas.
  Party size limits.
  Area permits/licenses, reservations, and trip permits, though these should be instituted only in special situations as a last resort.
  Trail alignment to minimize soil erosion, avoid wetlands, sensitive plant or animal habitat, and sensitive archaeological or cultural features.
  Trail alignment to maximize compatibility with adjacent land use and connecting trail use.
  Natural and artificial design features that restrict bicycle speed, such as barriers and speed bumps, which are not an undue impediment to other non-motorized users.
  Design features that enhance sight distance, e.g. locating the trail away from tall brush.
  Design features that minimize trail erosion: proper grades, turn radii, tread hardening, and drainage control.
  Wide or pull-out sections to facilitate safe passing.
  Design features for user enjoyment: loop trails, scenic destinations, picnic/camp sites.
  Barriers to prevent leaving trail. Block and obliterate (rehabilitate) unauthorized trails.
  

Trail User Etiquette and Education:

• In order to minimize conflicts with other trail users, bicyclists should know and use the established Rules of the Trail: - Ride on open trails only. - Leave no trace. - Control your bicycle. - Always yield trail. - Never scare animals. - Plan ahead.
  Bicyclists should know and follow applicable laws and regulations.
  Bicyclists yield trail to foot travelers, both animal and human. Yielding trail means: slow down, be prepared to stop; establish communication; dismount when appropriate; and pass safely.
  Opportunities to educate users include: audiovisual presentations; public service announcements prepared for television, radio and print outlets; community presentations; production of printed materials such as brochures and posters; information kiosk or trail head signing; trail information hot lines or Internet sites; bicycle patrols; widely distributing maps and guidebooks; and advertising by equipment manufacturers and suppliers that promotes responsible bicycling. Joint activities can provide rider education, trail planning, volunteer trail maintenance, or just plain fun interaction.
  Cross-country bicycle travel off trails is not appropriate.

Do any of you enjoy mountain biking? Do you follow those guidelines for etiquette, and do you consider actions you can take to mitigate any negative impact you have?