First of all I have a general dislike for any application that does not use the native look and feel of the operating system. Why does every piece of MP3 software want to look like an expensive stereo? If you're a PC application you should look like any other PC application. I'll choose my preferred skin at the OS level. Thanks.
Secondly, iTunes is too stupid to keep an eye on any folders I have added to the library. When I add new files or subfolders, I want the library to update itself. Very much like Google's Picasa automatically detects new images that were added, and updates its database.
After adding my original folder once more to the library it goes off and tries to download the album art of each song. I know I especially enabled this feature. I like it. But hey, why do this again for each and every song in the library? And why does it make the whole user interface become sluggish? It can't be that hard to do that in a nice low-priority background thread.
So why do I keep using it? Because I get free credits for the iTunes store with my ADSL account. And of course you need the iTunes software to use them. Maybe the guys up north are right...