It would be nice if there was a date/time stamp on the photos when you take them. Like if you tap the picture it turns around to show the date/time it was taken.
The date/time stamp and other "EXIF" info from iPhone pictures will be available to you once you import the pictures to a photo application like iPhoto.
Of course, I still like your idea of a tap bringing up some basic info on the phone display itself.
I too agree this would be a great feature all with the ability to add other meta data to photos (ratings, comments, etc) and have it sync'ed back to Iphoto (similar fashion as audio data is handled via iTunes)