I've been doing it for about four years now, and It's gotten to the point where I NEED to have an ipod or some music going, or I have trouble skiing. I find it inspires me to ski alot more aggressive, thus making me ski better overall. Interestingly, and I would like to know what others do, my music changes depending on the type of riding: park is rap, mountain is metal/rock/techno.
On the topic of tuneups, I'm neutral to them. They sound great, but two problems exist (at least in my gen. they could have fixed these): the clip to keep the mute button on the jacket lapel sucks and the button then falls into the jacket and gets hit when it moves around, randomly muting the music. Secondly, the mute button when exposed freezes, so when you try to push it in and out it only partially engages, muting one chanel of music and not the other giving a hollow sound that only can be fixed after fiddling with the button.
In conclusion, Ipods are very clutch for skiing.