The best response I can give to the original post is "Practice, practice, practice." Pretty much everyone has the "Oh snap, I need to unclip, but can't!" experience at least once when they first start out with clipless pedals. With some practice, you get so you can unclip them in time to avoid falling under all but the most unfortunate of circumstances.

As for downshifts while riding uphill, just ease up a little as you shift. Both of my road bikes seem to handle this with no problem at all.