#2 - PHYSICAL FITNESS. I am so out of shape, that I can rarely make a run from the top of the mountain to the bottom without pausing for a moment to catch my breath. Maybe it's the altitude, maybe it's tired muscles, but really, I think it's because I'm out of shape for skiing. BUT, if I had more of #1 (time), then I believe that would dramatically help out with #2. After all my trips out West this season, I feel MUCH better than I did before. My old jeans fit great again, and I have tons more energy.
Yeah, I'm probably quoting this one way too late (hence the right person will miss it), though I'm actually doing a course in sports physiology and just have to say that: If you have to catch your breath it's because you're out of shape and should (you really should, a healthy heart is a good thing) run intervals (since intervals is pretty much the only way to improve your heart's stroke volume which, in turn, improves your general fitness and prevents heart attacks). 4 times 4 is a good one, four minutes of running as fast as you can run four minutes, then three minutes of "active break", repeat four times. Do this twice a week and you will improve a lot.
If it's your muscles being tired (not you being short of breath) then it's because you don't ski enough. Best way to improve is by skiing, second best is my going to the gym and work out your legs (say four reps, four series with 90% of maximum, or something like that). Of course, stronger legs will make skiing an easier task for your muscles, thus reducing the need for oxygen and make you less short of breath. Hence just skiing will make you better, but I would add in some intervals as well.
Just my five cents... ;-)