[Brian]

Immediately after upgrading to 10.5.3, I had both of my machines be very unresponsive and heard a ton of disk writes chatter away. On the second machine, this happened even though I had no applications open at the time.

I have no idea what the system was doing - based on activity monitor, my best guess is that a background thread was updating all of the spotlight metadata for my files or something.

The activity stopped after 10-15 minutes on both machines and hasn't reoccurred.

I'm chalking this one up to the OS upgrade.