running mommy,
I've made those EXACT same conclusions about MTBing! It was like you were reading my mind. I'm a roadie, but have gone mtbing three times now and just love it! But it's an ENTIRELY different sport than road biking, and it still gets me every time I ride. I went on my third ride yesterday and I find that though I'm fit and can keep up with my friends, my fear gets the better of me sometimes, especially going down hills with big drops and large rocks and tight switchbacks, and that's what slows me down. I can already feel myself getting more comfortable and relaxed. The best part is, I go with my friend who's not ashamed to get off her bike and walk it through really technical parts and it makes me feel ok to do that too!