Great posts, Alex !
Trail braking on track explained by Keith Code:
http://forums.superbikeschool.com/in...08&#entry25618
Steering is less effective on loose surfaces like sand, and the front tire tends to dig into it rather than leading the bike in a different direction: it is way too easy to overwhelm that front tire.
That is why, steering is frequently accomplished by skidding the rear tire, so pointing the nose of the frame in the new direction while the front tire still rolls in the previous direction, like supermoto riders do even on asphalt.
Link to original page on YouTube.