In my experience, yes - it's a huge resource hog. Up until recently, I'd leave iTunes open all the time. After a couple days of being open without a restart, iTunes would have claimed ~1.2GB of memory. Pretty ridiculous. It's even worse if you use coverflow.
That being said, it's still my favorite audio player. It's one of only two programs I miss when I'm working on Linux.
That being said, it's still my favorite audio player. It's one of only two programs I miss when I'm working on Linux.