I honestly think I'm at a point where I need to do something to provide a better connection to the pedals, from both a safety and efficiency/power standpoint. Now, whether the right answer for me is pinned flats/grippy shoe or clipless, I don't know. It's proving hard to sort out without actually just taking the pludge and trying one or the other. I don't know that there's any one timeline for clipless that's right for everyone. It seems like there's a vast array of experiences--good and bad--with them. And I think it's perfectly fine to never ride clipless on an MTB and to stick with flats.
If I were to try clipless, it would likely be with a multi-directional SPD cleat paired with Shimano's M647 pedal, which is about as well reviewed as SPDs come. If I were to go with flats, there are handful of pedals that seem fairly well reviewed. Boy, some of them are really pricey though. Certainly, I'd stick to easier trails as I got used to them if I went that route.
As far as my road experience, I've run Look Keos from day one. While I sometimes fumble with getting clipped into them, I've never faltered getting clipped out or forgetting that I'm clipped in. So, I tend to think that the second nature part of it will come to me (although I also anticipate some falls). I'm more worried about what they'll do to my confidence, especially on unfamiliar trails. In an ideal world, I'd have both set-ups and could switch between the two as appropriate. But I'm not prepared to spend that kind of money right now on shoe/pedal set-ups. From that standpoint, I tend to think that the flats will prove more versatile.
While I don't think this attitude is universal, one common theme to a lot of threads I've read where people have switched back from clipless to flats is "fun." As in, I'm having a lot of "fun" with the flats. I want to have fun out there myself. That's key.

