The President of the United States often really seems to be a kind of elected Priest-Monarch. One area in which this is obviously apparent, is his ability to reward cronies and fundraisers with agreeable Ambassadorships overseas. Matt Yglesias, who is too wise to buy the wisdom himself, offers the official justificatory fig-leaf for this patronage:
I had always just thought of this is a kind of casual, widely accepted corruption. But recently I did learn the official story as to why this is good practice, namely that an important political supporter or a friend of the president is likely to have a much easier time of getting access to the Oval Office than any mere foreign service officer would. Thus, it’s arguably better for the host country to have a political appointee than a career FSO. Therefore, this practice helps build good-will and so forth.
Up to a point Lord Copper! It's true, for instance, that Jean Kennedy-Smith, appointed Ambassador to Ireland by Bill Clinton, found it easier to get a line to Tony Lake and the White House arguing that State should support an entry visa to the US for Gerry Adams in 1994, whereas Raymond Seitz, the first career diplomat to be Ambassador to the Court of St James in London, opposed the notion not least because Adams had not renounced violence. Seitz, mind you, further suffered from the fact that he'd originally been appointed by George HW Bush. (Seitz was accused, if memory serves, of "going native"; not an accusation ever levelled at one of his predecessors, Joe Kennedy.)
However, there are times - and they've been plentiful in recent years - when appointing Presidential Chums to plum posts has proved disastrous. Consider William Farrish, for example. In the years after 9/11, when the US needed an Ambassador prepared to explain and defend US policy, Farrish was an invisible man.
As The Economist noted Farrish almost never bothered to appear on the BBC's flagship political programmes. Given the sales job required to convince British opinion over Iraq this might be considered a pretty flagrant dereliction of duty. Not that his deputies were much better, mind you. And it wasn't just in Britain that this was a problem: US Ambassadors hid in their Embassies in Berlin and Paris and other european capitals. Doubtless they enjoyed the fine houses and the finer cellars, but they weren't doing their job. Of course, in some of those cases matters weren't helped by their inability to speak the native language. German is difficult you know?
You might say that the importance of the ambassador is less than once it was (though Charles Crawford might quibble with that) but there still remain times, even in lovely Paris and London when it matters that the ambassador be prepared to do their job. Even better, of course, is they're capable of doing so. That shouldn't be too much to ask.
UPDATE: In the comments, Anthony makes the excellent point that across large parts of the world foreign policy is really conducted by the US military. Robert Kaplan has written about how US generals act as "proconsuls" across the globe, from CENTCOM and West Africa to the Phillipines and Latin America. And so, yes, here too State is often bypassed. One imagines that HR Clinton, with her experience on the Armed Services committee, is likely to want, with Bob Gates, to have State and the Pentagon working more closely together. Still, the diplomatic corps retains an important PR and, well, ambassadorial role.
UPDATE 2: Commenters are smarter than me. Nadezhda correctly points out that Dana Priest's The Mission is actually the best book on the proconsular role of US generals. I don't know why I forgot that since not only have I read the book, but I reviewed it. Flatteringly, I think.