I just got back from my last day of skiing this season - "last day" because of the lack of snow.
When my daughter first started skiing, we stood around and watched her at her lesson. We didn't want to do that the next year, so we signed up for lessons at the same time, so we could all be in lessons at the same time.
Since then, we've done lessons every year. On the way, my wife and I have gone from from strong intermediates to the whatever the next level is (I hesitate to use the word "expert", which has lots of connotations. We ski blacks and some double blacks). Each year, I think that I'll reach the level where further instruction isn't really worth it, but like all the past years, I got a lot out of this year. The instructor who runs Olympic's race program got me to open up my stance a bit (ie keep my skis wider apart), which got my skis working more independently and enabled me to get more ankle angulation than I've had in the past. It lets me get a better edge during my carving, and "flow" much better.
The interesting thing that I've noticed is that there is a real reluctance among adults to take lessons. There are tons of intermediate skiers out there who are working really hard and not having that much fun, skiing the same 5 runs over and over. Not everybody has the ability or the desire to be a great skier, but I know that everybody could have more fun.
I think a lot of this has to do with people not wanting to look bad, or wanting to try something new. I don't understand that attitude, however. Sure, it's not fun to look bad, and it's hard to work around habits, but who wants to do the same thing year after year.