Of course, using a GPS may limit your ability to involve yourself in epic situations, such as getting lost in a whiteout and relying on your map, compass, and strong belief in your own badassness to get you out.
Fully charged batteries are supposed to run the eTrex for 18 hours, but the life is way lower in cold temperatures. My GPS did still work in a couple of really cold situations though. I don't keep it on unless I am actively using it to move toward a waypoint or to take a bearing. On the way up I turn it on, set a waypoint, turn it off. I've never been forced to use it. To be honest I've used it more for sea kayaking than for climbing.