Not sure if this will help anybody, but I have iTunes for Windows x64. A large amount of my slowness issues went away after fixing my permissions on my external drive and taking ownership of it. Doing a similar procedure on your Mac could very well help some of the people here (or completely disabling drivce ownership). Here is how I took ownership in Windows 7 Ultimate, and should be about the same for most versions of Windows:
-Find drive entry, right-click, select "Properties."
-Click "Security" tab
-Click "Advanced" button
-Click "Owner" tab
-Click "Edit" button (your username should be shown as an option in the window above this button, but click the Edit button first)
-In "Change owner to:" select your username
-Check the box for "Replace owner on subcontainers and objects"
-Click "Apply" and let it do its thing.
-Click "Ok" on the Advanced Security Settings window it brings you back to.
-Click "Ok" on the properties window it brings you back to to close it.
Note: There is sometimes something else you may need to do, as well. Open your drive, and find your iTunes/Media Folder/Music Folder that houses all of your iTunes files and folders, and right-click it. Select "Properties." If the little check-box for "Read-only" is still "lit-up," that means there might be a problem folder or file in there somewhere that still needs to be fixed. Look at each of your folders in your media folder to see if it has a lock icon on it. Just by trying to open that folder, Windows should ask you if you'd like to take ownership of that folder. Do it. If you find some files that are locked, like old iTunes apps, you can either take ownership of them, or, like in my case, delete them. Some of my remaining locked files were old backed-up iPhone apps I didn't need, anymore.
I had a couple of problem folders, for some reason, and my issues didn't disappear until after I fixed them. I assume iTunes was confused and probably spent a lot of its time trying to read/write from theses folders, and failing.
