I have been struggling for the last few days with iTunes, have read umpteen posts on lots of forums (Apple and NON-apple)... it's not just 50 people or so, but a minimum of several 100's WHO HAVE POSTED, so, we can be fairly sure, a minimum of many 1.000's are experiencing problems, since most are too apathetic to register and post...
After reading all this stuff, and spending some hours to try to get to the bottom of it: I do not believe it is an iTunes ERROR as such, but a 'function' which is having bad effects (hence no iTunes update as yet)... BUT I need some help from other iTunes users to verify this.
So, to make sure you have a clean install (although this is only a problem in some cases, but almost certainly Mike_Fuji's - along with, perhaps, a bad alias!):
1. trash iTunes and all aliases, as well as the following files in System/Library/Receipts:
a) AppleMobileDeviceSupport.pkg
b) iTunesAccess.pkg
c) iTunesX.pkg
(these are just 'receipts' that tell the system which items are already stored, and whether only updates are needed - when deleted, the iTunes installer will overwrite any already installed SYSTEM (not user) components. This is good, because any out-of-date or corrupted components will be replaced. Your library will NOT be affected!)
2. Empty the trash can and restart (just to be sure ;-)!!);
3. Re-install iTunes.
Fire up iTunes, and ALSO fire up Activity Monitor (System/Applications/Utilities). This is a little Apple-own "Task Manager" (for those of you out of the Windows world) that tells you what programs are running, and what kind of proccessor and memory usage they are using. IN ADDITION, you can examine a particular program/proces, and see exactly what it is doing... SOOOO, select iTunes in the list, and then 'inspect' (the blue 'i' icon up top); up pops a window... then select 'open files and ports' - scroll down to the bottom, and then...
Go into iTunes, but organise the windows so that you can see the Activity Monitor window at the same time as iTunes, and as soon as you get the "beach ball of death", have a look at the BOTTOM of the 'open files and ports' window... you should see at least one (and probably only one) line that is changing - on my computer, iTunes seems to be updating the resource forks on my video files (podcasts or films), which take some time to be read, before SOMETHING is written.... (see large amounts of data being read from the hard disk).
The GOOD NEWS is: it seems that whatever iTunes is updating/correcting, probably requires a certain amount of time, and then it should be done... but I could be wrong, and I'm not holding my breath :-)!!!
If you reply, PLEASE let me/us know what kind of iTunes library you have, since I think this plays a part...