Wikileaks did some astounding things. Truth should be revealed, and they helped to do so big times with their huge leaks about Iraq and Afghanistan.
Now, the diplomacy thing is a different story though. The world has a right to now what a democracy does in a war, but diplomacy always has secrets, and this one clearly was one-sided against the USA because most countries will have such files, some even worse.
However, it was very interesting to read it (personally I read the German SPIEGEL weekly, which is one of the two or three magazines which always get the wikileaks first). Interestingly the US "insights" on German politicians were a 100% what German journalists and people always knew, so seemingly their inside sources weren't as valuable as they thought in here

The green party does not have an attention-getting leader like Joshka Fisher was... Sigmar Gabriel is a good speaker... CDU and FDP don't suit each other although they're in one gouvernment... Guido Westerwelle is incompetent, arrogant and has a bad humor... Horst Seehofer doesn't know much about foreign policy and is a populist...
Every German who reads a newspaper once in a while knows these things. Congratulations USA for using covered spies and risking the trust of German politicians to get such information xD
Actually, if those files are what the USA know... it's very much the stuff you could read in any newspaper. Israel wants the US to attack Iran? SURPRISE! The USA don't know anything about North Korea either? Welcome aboard. Vladimir Putin has the behaviour and character of an alpha male? Hello Captain Obvious!
Yeah... really... that diplomacy stuff isn't worth that much publicity, it just shows that the US can't keep their stuff secret.
However,
Wikileaks should not be stopped. As a platform for anonymous revealing of publicy relevant information, they are incredibly worthy. If anything, those conservatives should stop ranting about it and finally acknowledge that truth shouldn't be kept hidden at all costs.
Many people and magazines already said that Wikileaks essentially is what everyone hoped of the internet - bringing more transparency and free information to the real world. It might be one of the best thing the internet has spawned yet.