It is not absurdly fast, but it is also not too common either; as most "advanced" skiers won't bother skiing that fast, because there really isn't much point in doing it.
At that high speed unless you have the whole race course, race skis and legs of steel, you cannot hold the ski's natural turn without skipping out, so you just end up going straight until you hockey stop.
It is the same as car racing. Perhaps you are exhilirated by just doing drag races, and you live your life a quarter mile at a time from stoplight to stoplight. But most "advanced" car enthusiast would rather spend their time turning, braking and going in circles, not just stepping on the gas for a bit then deploying a parachute.
So most advanced skiers would consider straightlining a run a waste of a run. They would rather crank out some turns, or at least look for a bump or a roller or a curve or something to mix things up. Actually nowadays most "advanced" would be offpiste and in the trees or in and around the rocks and moguls.
I happened to have the chance of a lifetime trip to ski over at flacau winkl (austria) and they had a "speed course" setup, where it's a roped off straight section with a starthouse open to the public WITH a radar speed trap at the bottom to prove your speed. Just tuck and go, and physics takes over. I hit 80kph=50mph, and felt in control and have gone faster before straightlining on other slopes. But it is faster than my my usual pace when taking turns and dangerous enough that if you wipe out, you are at huge risk to slide for awhile and possibly into a tree or other obstacle.
But then watching the next people go through, pretty much everyone is within a few kph of everyone else as long as they were about the same weight, had decently advanced skis, could do a decent tuck and then skiing flat and straight. The people who had race practice and could do a nice launch and a few skates at the top get a couple extra kph. But what's the point?
It is not really that interesting, the section just next to it with a few gates to weave around was more interesting.
But yea, if you really are just debating over speed and the accuracy of the iphone gps, just buy a radar gun (perhaps from a place with a generous return policy) bring it with you and just radar your buddies and that puts the issue to rest.
Edited by raytseng - 4/6/14 at 11:49pm