There is certainly no problem with mountain skiing - no special precautions necessary for that.
I often do watersports in my piece, and no real problems there either. Lace is permeable to water - the water just flows over and through it, and the lace doesn't offer any resistance to the water, so the piece is not going to be whipped off a la Hollywood farce or anything like that. The only real issue is making sure that the glue or tape is strong enough to withstand immersion in water. I always do a fresh attachment the night before with a strong waterproof tape like Proflex tabs, and I have not had any problems with scuba, windsurfing, wave surfing etc. I haven't done much waterskiing, but I would wear a bandana for that just in case, because of the additional pressure on the hairline if you go over and get pulled along by the boat for a while; same for rafting.
One other thing: I don't think skin-based pieces would be suitable for watersports. They DO offer resistance to water - if water gets under the base it has nowhere to go - so with those I could foresee circumstances where the bond could give way under pressure and the front of the piece could become detached. Not very likely perhaps, but I wouldn't want to take the chance.
Loving your facebra incidentally, Shookwun.