The problem started when I was puzzled why iPhoto on my iPad2 doesn't show the geotag info of the photos in the iCloud Photo Stream, while those photos' geotags show up fine on iPhoto on my Mac. Then I saw that they are only 2.8MP when they are supposed to be 5MP (taken with my iPhone4). This is not good.
The only way for me to push the real photo is to beam it directly from my iPhone 4. What's the point of iCloud then?