According to a thesis published in 2006, ski wax is snake oil. Leonid Kuzmin is the author of a couple of papers, both included in his thesis from Mid Sweden University (pdf), that demonstrate that many practices designed to decrease friction between nordic skis and snow are counterproductive. It is the authors assertion that waxing practices evolved when skis were made of wood and that a critical re-examination of these practices was lacking when wood was replaced with modern plastics. The data in the thesis suggest that there is no advantages to waxing skis. At best, the data suggests, an improvement in glide is observed for the first 200m. After this point, a waxed ski picks up debris increasing friction with the snow to the point where it becomes slower than an unwaxed ski. The thesis also pokes holes in two other commonly held beliefs, that wax protects skis from water penetration and offers protection from abrasive wear. While this work was done exclusively with nordic skis, it is the authors belief that the findings hold true for alpine skis.
It is not hard to find lots of passionate anecdotes refuting his findings, however I was surprised that there was no real scientific studies demonstrating benefits of waxing skis.
From the thesis:
Skis treated with any established waxing procedure loose their glide ability faster than the reference skis (dry skis).
A typical counterpoint found in internet forums:
I was in a hurry to get to Sun Peaks a while ago. My skis needed waxing but I didn't do it so we could get on the road. On our first day I was having trouble getting a good slide going and I had to continuously pole and skate to get up over a hump to get to a particular face. That night I waxed my skis. The next day with essentially the same snow conditions I flew over that hump so fast I had to brake at the top, and I certainly didn't need to pole or skate. Wax works.
Despite this thesis, now 5 years old, most skiers get their skis waxed or do it themselves. I wonder if this is a case where the mantras and anecdotal evidence are winning in terms of acceptance or if the studies just did not get publicized well. Perhaps the first 200m where a waxed ski glides better is the source of much of the anecdotal arguments for waxing. Personally, I think much of the resistance to accept these findings is due to the fact that waxing skis can be an enjoyable process. Waxing your skis gets you excited to go skiing. I actually miss it.