Some good points raised so far

I see mountain biking as being very similar to bush walking. I go bush almost every day and normally do an epic bush ride on a Saturday or Sunday and often my rides involve parts of tracks that I've walked previously. I find it a bit offensive when a trail I've ridden for years is suddenly closed to mountain bikers due to "degradation" of the bush when clearly, the people who made this decision (e.g. Kingborough council in the case of the Alum Cliffs track) have no idea what they are talking about and have sought no opinions or consultation from the users affected (such as the Kingborough Bicycle Users Group, Hobart Wheelers / Dirt Devils, Southern Pedals etc.). What makes things even more hypocritical is the insertion of drainage, steps, benches etc. along the Alum Cliffs trail (and other urban trails) which in my opinion "degrades" the bush much more than the odd mountain bike tyre mark!
Anyway, those are urban trails so it doesn't cramp my style too much (I just wanted to point out the lack of care for the opinions of particular user groups in that case).
Most tracks I ride are far enough out of the way to not be affected, yet.
One last note: I'm heading up the west coast to do Queen Hill, Montezuma Falls (part of the Wildside MTB) and others around that area. What a great opportunity to ride to East Pillinger along the old Bird River track and check out the ruins of the old mining / pining town, or so I thought! According to PWS: "Vehicles, including mountain bikes, are not permitted beyond the barrier on the northern side of the Bird River Bridge." Has anyone here walked to East Pillinger? Does the track follow an old railway line and if so, is there an obvious reason why mountain bikes should not be allowed?
Ok, time to stop ranting!