davereporter wrote:
1) Slip wearing - personally I don't have a problem with a non-lacy half slip. A lacy slip would make me feel weird and most of the tube style slips ride up because they don't allow enough movement.
Since, if properly worn, the lace on an underskirt (to avoid the use of that "other" term) doesn't show, so what's the bother? The lace, actually, being a bit more coarse, helps keep the underskirt down and in place so things don't ride up (they shouldn't, anyway, if the size is gotten right). I have two moderately long lace-bottomed ones (21" / 53cm) that I wear under my longer skirts and I've never worried about them showing. I also have one the same length that has a slit in it (that I wear towards the rear) that works well, too. If I'm going to be wearing something really flowing (like my peasant skirt) I'll wear the one with the slit in it (no lace) so I can really get my legs moving; with the other skirts, it doesn't matter so much, so either will do. In short, if it doesn't show, why care. The thing is a functional piece, not a show-piece.
davereporter wrote:2) Skirts whilst hiking - great. Did it when in Hawaii and had no comments. The difficult is that if you have an unpleated straight skirt (such as the cargo I was wearing), climbing over rocks and streams can be a bit of a problem.
Definitely in this case, shorter and more flowing (wider hem) the better so one's legs can really stretch and move. Jumping around on rocks takes work, skill, and concentration. Having your garment get in the way is a "Bad Thing". I supect that wrap-skirts would work very well in this regard as the hem is free to move in all sorts of ways.
davereporter wrote:The only advantage of pants was that I was not at risk of flashing my knickers

Unless you're "going regimental", modest briefs shouldn't pose a problem. You may actually show more at the beach (many women do).