This topic started coming up in one of Dawg's reviews, but I didn't want to hijack that thread any further. Dawgcatching commented that his new Sultan 94 skis were "extremely railed" out of the wrapper and that many of the Dynastars were delivered with un-flat bases and a desperate need for a full tune before being skied. Many people seem to agree that new skis should be tuned before being skied (although some disagree). The new-ski tune makes sense to me, but there are many levels of tuning (with the most significant being a full base grind, edge shaping and polishing and sidewall shaping and polishing -- easily setting one back $100 at a good shop).
I have two new pairs of skis in my house right now that have not yet been skied. One pair is the Sultan 85 and the other is the Nordica Victory. Neither of these are particularly fat skis (85mm waist and 78mm waist), but both of them are a little concave in the tip and tail while perfectly flat underfoot. Mind you, my true bar has not been delivered yet and I was just using a metal straight edge to check these, but with that instrument I could see the differences in flatness as mentioned. I would guess that the gap under the straight edge was less than half a millimeter at its deepest point -- I could not slide a credit card under the gap, but I could see light coming through the gap.
I plan to thoroughly wax them, shape and sharpen the side edges and make sure the base edge bevels are acceptable before anyone gets on these skis. However, I would prefer not giving them a stone grind if not really necessary.
A forum search pulled up a number of threads about concave bases and many people were suggesting that a slightly concave base is not a problem for a recreational skier as long as it doesn't impede the tuner's ability to set and maintain the edges.
I understand that a concave middle will not affect edge tuning if the base is flat near the edges where the edge guide rests. But if the base is concave from edge to edge with a half millimeter space at the deepest point of the crescent, will this affect edge tuning so much that it will be a problem for a recreational skier? How flat do they really need to be?