IPTC
that's the stuff it keeps, not sure how much of it like shutter stuff etc.
generally people have issues with changing the file itself - like the crop, or there was noise etc, and the thumb doesn't update itself right away. but it should change fine. the title becomes the main link, which then breaks in google etc. though if you just uploaded it, i wouldn't worry about that either.
the only thing i send with the file is - title, artist name, description, keywords. those are the things the site recognizes.
----Mike Savad
http://www.MikeSavad.com