A public wave has been set up on Google Wave for discussion and posting of all things MTB. If you are new to Wave, you can access and follow this wave by typing the following into your search bar (at the top of the left hand panel)
with:public "Calling all mountain bikers"
Once you get your results back, you can follow the wave and add yourself to it and begin to post. There are currently 54 users on this wave and it seems to be growing by the day. Thanks to @trialsoflife for setting it up!