Bloomsbury has release the inside cover complete with plot summary. I've read it myself and I dont think its much of a spolier (the US cover usually has alot more spoilers thats why I think they havent posted it yet, they didnt for OotP) but I'm posting it here as a spoiler for all you guys. If you'd like to read it heres the link.
http://www.bloomsbury.com/harrypotter/content.asp?sec=4&sec2=1&unart=yes&artTitle=Back%20Cover%20Copy%20ReleasedI'm also posting as a spolier, a close look at the HBP deluxe edition cover. This is on Scholastics site. Heres the link
http://www.scholastic.com/harrypotter/funstuff/art.htmI'm also posting a comment I read about the Deluxe Edition. On a forum somone said that the man is the man spoken about behind J.K.s door last year. The info said
He looked rather like a lion. There were streaks of grey in mane of tawny hair and his bush eyebrow; he had keen, yellowish eyes behind a pair of wire-rimmed spectacles and a certain rangy, loping grace even thought he walked with a slight limp.
If you walk with a limp you mostlikely carry a cane, am I right so it is possible the "X" character in this picture is possibly the character spoken of, possibly why we dont see his face.