In a general way, there is nothing in the to-be-released Wikileaks diplomatic correspondence that will surprise anyone. All countries say things in their confidential diplomatic correspondence that they don't say in public. The advance notices have allowed the United States to confer with the countries that may be annoyed by this. Some may feel they can score some political points, but the advance notice helps to limit that score.
The documents will contain expressions of no confidence in Hamid Karzai, possibly also David Cameron, Dmitry Medvedev, and others. There will be bad language. There will be some juicy bits that will make it into the MSM. The blogs will add one or two more.
It is harmful to diplomatic candor that the material has gotten out. But it appears that the leak was via one person who is now in custody. It will, very likely, happen again, but nobody knows where or when it will happen, so they will, after a short period of caution, proceed as they have in the past. Interactions between nations will require that.
One of the mistakes that Wikileaks makes, I think, is to release far too much material at once. Does anyone believe that anyone has gone through their previous two releases in detail? On the other hand, Wikileaks' credibility would be damaged if they picked out only the good parts.