That is interesting, so are you saying that it the photo was taken in Time Zone A, then imported to the Mac via usb in Time Zone B, iPhoto will tag the photo with Time Zone B?
I noticed that in two situations:
- when importing to iPhoto from iDevices (iPad) with location service enabled in the iPad using USB (the iPad seems to interpret the timezone of the photos as the timezone of the new location)
- when importing from a camera with a different timezone setting. If the dates don't carry timezone tags, iPhoto will assume that the timezone to be the current system time. The results may differ, depending on the kind of timezone setting the camera supports and whether importing directly from the camera or from the card.
When I am travelling between timezones I usually take a picture of a clock at the beginning of each event to be able to check the timestamps after importing the event to iPhoto or Aperture.
Aperture allows more control over the interpretation of timezone settings, btw.