iPhone (1.1.2, 1.1.3, +) requires a USB 2.0 connection to Sync

The laptop which I have been using to sync my iPhone only has USB 1.1 ports (PowerBook G4). The specs for the iPhone says it only supports USB 2.0, but I've been successfully syncing for months. That is, until I upgraded to 1.1.3 firmware. After that, syncing would always hang and sometimes iTunes wouldn't even recognize that the iPhone was connected. I noticed that the following messages would appear in the system.log every time I tried connecting the iPhone:

AppleUSBOHCI[0x13de800]::CreateGeneralTransfer - trying to queue to a stalled pipe
AppleUSBOHCI[0x13de800]::DoIOTransfer - error 0xe000404f queueing request

Searching the internet found that others had solved the issue by going through a USB 2.0 port. So, I bought a PCMCIA USB 2.0 card at Circuit City, plugged it into my laptop, and now I'm syncing away without any problems.