Currently Vista, but iTunes didn't recognize any of my installed codecs under XP either on my other system. If I try to drag and drop a divx file into my iTunes library it does not recognize the file, every other media player installed on my system (and I have quite a few) has no problem finding all my codecs.
Also you don't have to re-install to see that Cover Art Downloading requires a iTunes account (despite the fact that this is a common feature in other programs that have no such requirement -- I personally use Picard for all my coverflow tagging). To see it, simply go to Advanced --> Get Album Artwork and it'll bring up a little dialog box telling you so (unless you were already logged in when you selected it).
I'm told genius playlists have the same requirement, but I have avoided upgrading to 8.X.X versions of iTunes simply because it fails to add any new features I'm interested in (at least not according to the release notes). I do not need a new visualizer or genius playlists.
Also, somehow, the Winamp Install file (which I think is a much more fully-featured player, even if it is a bit bloated itself) clocks in at about 8 megabytes while itunes is a whopping 80. The actual iTunes install is 82, while the winamp install is 25. Still, iTunes seems fairly . . . large. Unless all the iTunes store artwork is stored client-side, I can't really figure out why it is that iTunes takes up so much space or why it runes 4 separate background processes instead of just 1.
Sorry, it's really hard for me to talk about iTunes without it turning into a rant.

That said, I really do love my iPhone and I just wish the two weren't married together.
Edit: Oh, for the sake of fairness, I suppose I should clarify: It's the podcasts that you get through the iTunes store that require an iTunes account. It effectively makes you "pay" $0.0 for them, so you need to have the account made to get any of the free ones. You can still get podcasts directly without an iTunes account if you have a URL linking directly to them.
It's the same thing with Appstore apps that are free still requiring you to have an account. No free apps for people without credit cards (I have one of course, but I wonder what all the people using pre-paid because they failed their credit check do).
So, not to be misleading, you can do podcasts without an itunes account, just not any of the ones hosted on the iTunes store . . . Cover Art and (
afaik) Genius Playlists also require the account.