That said, I agree with OP's point about iTunes's performance in Windows. It is - quite frankly - terrible. So much so that when I switched over to OSX, I opened iTunes and marveled at how quickly it could actually do things.
I have an iPhone and enjoy it, but I've only played a movie on it once or twice in the time I've owned it for this reason. This is true of most people I know with iPhones, and it will similarly be true for iPads. It's a glaring problem that Apple's doesn't seem interested in solving; they'd rather you re-purchase every DVD as a movie from their store, and then be locked in to their platform or else lose your content.
I've got most of my DVD collection in there at this point, and I actually find it fairly pleasant.
Well they work well for playback, but I've yet to find a comparable alternative to iTune's music library/organization features. You may have a point about movies and such - I tend to play them in VLC, and organize them according to folder in my external HDD.
As a for instance, I want a music player that handles flac and ogg files and that I can access in a terminal. Low memory usage is important to me also. I use cmus on a Mac, and I like it quite a lot.
http://code.google.com/p/beets/
It has an MPD clone player built-in, so you can use ncmpc with it if you want. Or just keep using cmus.
I mean you can buy music from Metallica and The Beatles in FLAC format. If Metallica and The Beatles are out ahead of you on some aspect of digital music, it's time for a rethink.
FWIW: I've got iTunes running now; it's been up for about four hours, playing music and I did a sync of my iphone and ipad. It's bouncing between 45 and 55MB of memory [1].
[1] (library: 14,000 songs; 300 movies)