I have a roughly 2 year old Macbook (10.5). I have iTunes 10.
When iTunes is playing MP3s, I see CPU usage of the iTunes process in the system monitor ranging from 65%-75%. When I pause the music, I see CPU usage of about 65%-75%.
I do not have any visualisations going, to my knowledge I have not turned on any CPU destroying features, my music library isn't tiny, but it's hardly huge (3GB). This is mildly annoying when I'm plugged into the wall as I only have slightly longer compile times, but if I am out and about, this is a major drain on the battery.
Using VLC I see CPU loads of ~= 10% at the most when listening to music and generally lower.
What the heck is iTunes doing?