Yes iTunes is much more processor intensive. It was using 20% of my dual cpu cycles until I turned look for album art off. I have a few albums with no artwork and I guess it keeps looking. The visualizer is also more demanding. I can't get more than 28 frames per second driving my 20 inch LCD.
iTunes 7 is completely buggy for me. Visualizer doesn't work, and album art shows up when it feels like. Windows hiccup like the thing is starved for RAM, but Activity Monitor shows plenty of RAM available. Even with nothing else running, it is a total dog.
Interestingly, it's got worse for me since I first installed it. It's acting like there's a memory leak, but as D*I*S_Frontman said, it doesn't seem to be taking up a considerable amount. Weird. I'm gonna keep my eye on this one and see if it's clashing with another app or something.
One thing that has helped mine is to go into the iTunes store, go to the Advanced menu and click 'get artwork'. With mine it began to go thru my 7k tracks and it took a good half hour to grab the artwork required. Since then it seems a bit better, tho still not as fly as iTunes 6