iPhoto2Gmail was installed directly into the iPhoto application bundle in the PlugIns folder. This was a necessary evil back in the dark ages, since iPhoto didn't look anywhere else for plugins. After Apple released an official API, later versions of iPhoto began looking outside the application for plugins.
I've been meaning to change this behavior for quite a while, but didn't want to break backwards compatibility. With code-signing becoming more and more important, and Lion on the horizon, I finally made the change. As of June 30th, the iPhoto2Gmail v1.1 installer will place the plugin in the Apple sanctioned location:
The new installer also removes the plugin from the old location. This change helps us be good Mac OS citizens, as foreign app bundles shouldn't be messed with. Unfortunately, this may break v1.1 for folks with legacy iPhoto versions. I've tested as far back as iPhoto '08 with good results, so it might be time to update!
The uninstaller has also been updated to clean up both locations.
Note: Aperture2Gmail's installer doesn't need updating as it was always well-behaved.