Mountain Biking Forums
Sadly, following the demise of pedalbite.com, if you're looking for a forum to ask questions or put out some ideas on mountain biking in Tasmania, the choices are pretty lean as most riders seem to use facebook for updates and sharing of knowledge nowadays.
With that said, Bicycle Network Australia still operates quite active forums, including one for Tasmania, but my impression of it has been that it is more focussed on road riding.
So nowadays, if you're looking for mountain bike community discussion, I'd recommend trying facebook. Hobart MTB Rides facebook group is probably the most active if you're looking for someone to ride with down south outside of the clubs.