When I connect my iPhone 3GS to my MacBook Pro, iTunes "freezes": the spinning beachball appears, and it will not respond to any mouse clicks or key presses. Activity Monitor shows iTunes as "Not Responding".
The iPhone indicates that it is being charged, and otherwise seems normal.
When I disconnect the iPhone, iTunes immediately returns to normal operation. Connect again, and instant freeze again.
I have rebooted the MacBook, and have reset the iPhone (held home+wake button until it reset). No help.
If I run Xcode (I'm an iPhone developer), it sees the iPhone and I can install and run software on the phone. So the problem seems to be isolated to iTunes, and not to the Mac as a whole.
Everything worked fine yesterday. I haven't installed software or changed anything since the last time I synched.
iPhone 3GS is running version 3.0.1. It is not jailbroken.
Mac OS X 10.5.8; iTunes 8.2.1 (6)