But then again, any old USB mouse will work on a Mac, and OS X supports the 2nd button and scrollwheel. I don't see the big deal in the fact that Apple can make one itself now. Oh, besides the $50 price tag.
Bonk, I seriously think your download was bad. My copy of iTunes on my laptop works just fine, even when I run it at the same time as SFC, ecxept then there's a little more time between songs, but other than that I don't notice a thing. I never paid attention to CPU or memory use though. Are you running the visualization while you're looking at the CPU usage? iTunes's visualizations are all hi-res when windowed and they'll suck every clock cycle you've got. Also try setting the priority for CPU usage a little lower. It just sounds like your system's weird!
Also, what version of iTunes are you basing your judgement on? I've never installed anything earlier than 4.7 on my systems, and my Mac's got 4.9 on it now.