If you're feeling up for a safari (har), go to your iPhoto Library, right-click -> Show Package Contents, and check out the sizes of each folder inside of here.

If you're feeling up for a safari (har), go to your iPhoto Library, right-click -> Show Package Contents, and check out the sizes of each folder inside of here. (the terminal command 'du' or the freeware GrandPerspective.app works well) Pay close attention to the "iPod Photo Cache". Any sync to an iOS device that requires a down-res means a huge volume of quasi-thumbnails get stuffed here, one set for each target resolution.