Avoid USB with large libraries in iTunes
For as long as I have been using it, I have been having problems with iTunes stopping playback due to lack of CPU resources. I have long thought that I was just hammering the machine too hard and that it was annoying, but maybe just to be expected. Not anymore.
My music library resides on an external 250GB drive, with USB2.0 and FireWire connection options. Mainly because I keep the USB hub 'n cable spaghetti in a bunch at the back of my desk, I opted for the USB connection, because the FireWire port is located on the left side of the laptop, too close to the keyboard for comfort.
Just acting on a hunch, I decided that since I have been using a wireless USB keyboard anyway, as well as a PC-card connected CD-ROM drive sticking out on the same side, the comfort argument is not valid anymore and that it might be a good idea to switch the drive to FireWire.
The hypothesis is that the high CPU burn of iTunes and other applications has something to do with the fact that I have a ton of gadgets hanging of USB ports. It all works, but it eats cycles. since FireWire is a standalone bus system, it will need a lot less resources. I don't expect a big speed gain, other than what is achieved by not having the CPU clipping at 100%, but it is still worth a try.
A reboot later and I am now due to smack myself on the head for not figuring this out sooner. iTunes' CPU usage used to jump to 90-100% on almost every use of the interface, and then again at every change of song. It now barely gets over 35%. I managed to push it to 65% by having it scan the entire library for new songs.
Moral of the story: if you use iTunes and your collection is of a significant size (which seems to make almost all operations expensive for some reason), avoid USB connections to your storage media.
(note: Apple users can stop their sniggering in the back, now. I know you will have been using FireWire as a first choice anyway)