There used to be a photo of me that was associated with my Gmail account, it was displayed during Google Video Chat sessions.
Today, while testing iChat, I signed in to my Gmail account from my MacBook iChat client.
Afterwords, when viewing my Gmail account on my PC, I found that the Fast User Switching image from my MacBook had become my Gmail account image -- presumably because iChat uses that image as its default chat image.
The original Gmail account image was gone.
Evidently the "Jabber" transactions that seem to underlie Google/iChat credential exchange also propagated my account image to Gmail via iChat.
It's a good thing I don't have exotic tastes in user account images.
12/25/09: Still a problem. This time I think it propagated via MobileMe until it now shows up in my iPhone as my personal picture! The picture I used to have is gone.