My SS, AaEG and FF are bent also. I don't have RoF and although Unapproachable East has been at the FLGS for two weeks I haven't picked it up to see if it suffers also.
It seems that of late wizards have been putting out a lot more titles with hard cover than they would have previously. If AaEG, RoF and UE had followed their predecessors they would have been softcover. They are no doubt finding that hardcover books sell more copies at a higher price than the softcovers.
I don't mind that more books are hardcover, I prefer the durability, but the cheap bending hardcovers are pretty poor form. I'm suspecting that some executive at wizards or elsewhere has decided that margins and profits can be improved by changing the way they do covers.
Ghostwalk is probably at the printers already so if they haven't fixed the problem yet it is probably too late.
I would like to say that I won't be picking up the 3.5E core books when they get here if they too suffer from the problem. I would like to say it, but I know that its not true and instead I will just get anoyed and stand in front of the shelf for longer before reluctantly handing over the cash anyway.