At aboc, we do coach MTB'ers, but don't do skills work, here's a nice bit of synergy
Jess and Norm Douglass run, by all reports, a great MTB skills development program, I won't prattle on about it here much because although I've heard good reports, and have spoken (email) to Jess, I haven't actually met them or been on one of their courses myself yet. I'd probably benefit a lot from doing one though, so will have to give it a go and maybe coin the phrase 'ungumby a gumby'.
Have a look at their site :
I'm going to refer any MTB'ers who want to do skill development to them, I think they're offering something quite unique and valuable to the MTB racing and trail riding community.