You may not be able to distinguish between a well-tuned ski and and really well-tuned ski, vterp. But you will definitely notice a poorly tuned ski (whether you can put your finger on exactly what the problem is or not). It's like a car--a novice driver won't detect the subtle suspension tuning nuances that an experienced race car driver would feel, but he'll certainly notice worn-out shocks, grossly worn brakes, or a flat tire!
Most good skis come out of the wrapper a lot better than they used to. But they still could have major problems--particularly edge high ("railed") or concave, or base high. These problems you will feel! In the former case (edge high), your skis will feel grabby and twitchy, and very hard to manage. In the latter case (base high), your skis will feel "swimmy," hard to get to grip--and very hard to manage. Many novice skiers just think they're skiing poorly, when the problem is a badly tuned (or untuned) ski.
So it's worth checking, at least. Beware, though, of giving your skis to "your-neighbor's-kid's-buddy-who-works-in-a-rental-shop" (if you catch my drift) to run over the belt sander. An inept or uncaring hack can quickly ruin a ski on a belt sander--or even create the concave or convex base you want to eliminate. Instead, take them to a good shop and ask them to check the bases with a true bar. If they're good, they'll do it at no charge, and show you what they're looking at. If they show you that your skis need work, get 'em tuned, preferably on a stone grinder, by a conscientious and experienced technician who takes pride in his or her work.
They'll also ski better when waxed properly. Wax isn't just to make your skis faster. It will make them more manageable as well--easier to balance on, and easier to turn, guide, and twist into a braking skid when needed.
My strong recommendation for everyone is, at the least, to get your skis well-tuned, and then invest in a few minimal tools, supplies, and skills to keep the tune maintained. At the minimum, a good diamond stone and some wipe-on, rub-on, or spray-on universal wax, plus a quick tutorial on how to use them, will keep your skis' performance light-years ahead of the typical skis most people ski on--with about 5 minutes of your time each day you ski.
Edited by Bob Barnes - 3/9/2009 at 08:56 pm