According to its manual (Sorry, the forum won't let me post a URL, but you can find it on Canon's web site) the S100 can not save its logs when using an Eye-Fi card (Page 114 of the manual):
If "an Eye-Fi card is inserted in the camera, you will not be able to save GPS log files."
I'm curious why this is. Is the battery life just too bad with GPS *and* WiFi running?
