iPhoto stops syncing photos from iPhone

I just noticed that iPhoto was no longer syncing new photos off the iPhone. As you can see in the image above, when the iPhone was plugged in, nothing shows in the import window, although there really are photos there!

From the number of pictures left on the phone this has probably been going on for about a week or so. I tried downloading them using Image Capture and it appeared to see them and looked like it was downloading them, but ever nothing arrived in the download folder.
After searching the Apple discussion lists fruitlessly, I gave up and simply rebooted both the computer and iPhone, and everything magically started working again. This hasn’t been the first time I’ve rebooted in a week, so it must require rebooting the iPhone as well.