i'm not sure if anyone else does this, but personally i did this myself and i thought i'd share with all of you ns'ers..
so on my ipod, i usually just get a lot of music, and just add it to my ipod.. like entire discographies. but, its impossible to create a playlist on your ipod while you're listening to it (unless you use the on-the-go thing.. but once you plug that into your computer you pretty much have to start a new one.. and then you end up with like 20 on the go playlists). anyways, my solution is that while listening to a song, if i'd like to add it to my ski playlist, i rate it 3 stars, and then since i have a smart playlist that automatically adds songs that are 3 stars, i have a on-the-fly ski playlist that is very legit.
spark notes: 1) create a smart playlist on ipod. 2) rate songs that you like to the number of stars in your smart playlist. 3) have live updating playlist(s), and fun