The Wikipedia article on SHA-3 says that Keccak has been chosen but the standard hasn't been issued. Does this matter?
That is, can we just assume it's going to be as specified by the submitters (specifically for SHA-3-256 it's the Keccak-f-1600 permutation, in a sponge construction with r=1088 and c=512 and the pad10*1 rule)? Or might NIST wind up tweaking something, meaning we might have to re-hash a bunch of things if we made this assumption -- which, depending on application, could be inconvenient.
(EDIT: of course, waiting is also inconvenient, thus there is a risk-benefit question here -- again, depending on application.)