It's funny...I think it really does depend on the individual. For some people, certification processes and being up at the hill every day really wear on them. I never had this experience. For me, though I loved teaching full time, what was difficult were the financial aspects and the consequences of doing hard labor (at my mountain, we helped ski patrol with fences, shoveling, etc., on top of the obligatory skate-skiing up hill, picking up and carrying 3 and 4 year olds, etc.)
I started teaching on weekends last season, but after about a month of it, quit my 9-5 job to instruct full time. I've coached and taught swimming for a long time, and teaching is something I love, so it was a natural choice. It was more fun than I've ever had in my life. I figured, I'm young, no kids, no mortgage, no debt... there will always be office jobs there (this was of course before the job market was truly as terrible as it is now).
So, I took the big plunge and started living up on the mountain full time. There was not a day that I regretted my decision (during the season at least...now it's summer and I'm looking for a more professional job again)... days were filled with laughter, singing, comradiere, and face shots, and I worked on a smaller regional mountain (albeit with some sick terrain), so we'd often have the place to ourselves on a midweek powder day.
But, I think if you're going to instruct, be a liftie, etc. you should go into it with eyes wide open... realize that you'll be broke, that you will get tired, that it will be a very different lifestyle... before the season, I had never chopped wood, helped haul a car out of a snowbank, or shopped at a discount grocery store. I'd never lived with or been around people who primarily didn't have college educations, or people who considered not having health insurance to be normal. So, culturally, too, it was a little bit of a shock.
Buuut...that being said, I got to ski a ton. And I spent my time with amazing people who became like a second family to me. And skiing never got old. Of course, after being up at the resort 25 days in a row, you say to yourself, okay, today I'm going to use my day off to do something other than ski, because if I don't go into town and do laundry and hydrate today, I'm really gonna regret it... so then you go and sit in the laundromat and read and drink lots of hot tea and watch the snow fall and convince some boy to give you massages so that your back will feel less compressed and you maybe will get to huck something tomorrow, and wish that you could be up there, but you remind yourself that your knees and ankles and shins will thank you. And some days your body is so tired that you need to go to sleep at 7 pm. Literally.
For me, I would never take that experience back. It's one of the best things I've done with my life, ever. And, it's a lot of fun. But it's financially difficult, and you have to give things up. You've got to realize that organic produce is not the norm, and that you just might have to eat instant oatmeal a lot of days in a row... and that you will be tired, and broke. And that you may or may not get sick of skiing (because, as people noted above, some people do get sick of it.)