iPhone (1.1.2+) 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:

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.