GPS is perfect for marking points.... we used one to mark a couple of new runs at Mt Buffalo....(yeah yeah i know, where, how, why would you bother???) on the back side of Dingo Dell.....we were able to set markers over summer and find them again during winter without no troubles.
(oh and incase you were wondering we marked out 4 new runs, the longest was a 1km long intermediate run, and no they werent cut...although i did ski one of them)