People are talking about potential damage from the recent release by Wikileaks of thousands of State Department Cables, and I think that they are missing the big picture here.
For all the chest pounding about how this is damaging, the reports this far are either not news (What, you mean Berlusconi parties and spends lots of money?), or more embarrassing than damaging (What, you mean that the Arabs hate the Iranians, as they hated the Persians for the past 3000 years).
The real issue here is that this is a natural consequence of over-classification.
Basically, since everything gets classified, and in the interests of communications between organizations, tens, if not hundreds of thousands of people get access, and they that most, if not all, of the data that passes in front of them is stuff that is either already public knowledge, or absolutely innocuous.
It makes people casual about restricted data, so they are more likely to mishandle it, or, as in the case with Wikileaks, they feel compelled to share it with 3rd parties because they feel that it should be public data.
The solution to this problem, and it will be one that the US state security apparatus will almost certainly eschew, is to classify less data, because tightening down on data more just makes the problem worse.