I posted about iPhoto and its absolute hoarding of file data, even if you prevent it from actually importing the original photos. It maintains its own file structure so that if you move a folder, it erupts in protest next time you try to access the pictures. This is understandable enough, but you can't educate it. You can trash the iPhoto version but it still remembers it was there and complains, even when you're trying to import the new locaiton. Of course, all your modifications get trashed. Good reason to stick with Photoshop for that.
Here's the post at the blog Google isn't speaking to right now. The Dave Keys fun Blog Post on iPhoto