The Share button brings up a list of all the installedapps that can be used to share or exploit a photo -- for example, if you install Evernote on the camera then this button will give you the option of creating a note out of the photo you're looking at.
The more we scan it, the more we realize that the list of winners reads like a who's-who catalog of apps we know we want installed on our Dreams out of the gate -- and more importantly, it looks like Google has a great way here to encourage best-of-breed Android development over the long run.