Flickr users? Ever thought how it was slightly annoying that your home page displayed your photos in reverse date uploaded order (regardless of whether you were just doing a bit of catching up or moving across a whole load of archived snaps or slotting some in that other people had sent you) and that the Flickr Organizr didn't have a means of editing the upload date?
Well, head on over to h4ppier photos - it's still in beta but has all the tools to edit all that EXIF data (including, crucially, setting date uploaded = date taken) and get your home page looking the way you want it again. Single photos to batches of 500, it can be done. Also does tags, sets, groups, sizes, etc and so on.
Worth a look IMHO :)