I wear my UK's hiking and walking all the time. Never had a problem with the apron getting between my legs. Of course I take long strides and so 'kick' out the material quite a bit while walking. In fact the wider apron of a traditional kilt is somewhat restrictive when I'm really moving.

I've never noticed a problem with the pleats poking my backside either, and I mostly wear my workmans. I do sit so that the pleats are pretty flat under me though, but thats mainly to inhibit wrinkling.

In fact the only problem I have with the wearing of a UK is that in narrow chairs the cargo pockets are in the way. Even then its not as bad as if I was in cargo pants and had loaded pockets, and fortunately I can just flop them around to sit where I need them.