Normally, I'd be the last person to talk about composition, f-stops, and even cameras in general - mostly because I know next to nothing about them and don't particularly have any interest in them - and yet here I am, writing my first blog post of the year on blurry backgrounds and why they may or may not suck. Thanks Arturo.
So Chris Knight, the author of the two part article about composition, really seems to hate bokeh. Or Boke, however you want to spell it. He goes so far as to say that a focus on bokeh (pun entirely intended) can make for lazy composition and can ultimately make your photography flat-out bad. So what exactly is bokeh, and is it as bad as Knight says it is? Short answer: no.
Bokeh, in terms that even I can understand, is the "aesthetic quality of the blur produced in the out-of-focus parts of an image made by a lens." Here it is in this pretty picture of a bench. See all those lights in the background? Bokeh.
As far as I can tell, there are a few reasons why a photographer would choose to use such a shallow depth of field to create the softly blurred background images that result in bokeh. One such reason is that you may wish to isolate the subject of your photo - in this case, that lovely bench - by separating it from the background. Here, even though the lines of light are forming something that looks just like one of Knight's "golden triangles," the focus of the picture is clearly on the bench. If the lights in the background were sharper and more in focus, the bench would not seem as isolated.
Another reason for bokeh could be to give the illusion of motion in pictures. If I'm correct, by combining a shallow depth of field (in this second picture's case, only bits of the windowpane are in focus) with a longer exposure time, you will get a slightly elongated bokeh, which gives these cars the appearance that they're actually moving. I think it's pretty cool, and when you take a few of the things that Knight said about composition into effect, I think that they're actually both pretty good pictures, bokeh and all.
To be fair, I can see where Knight would have an issue with having an "obsession" with bokeh. Too much of a good thing is, well, never a good thing. Bokeh is pretty, and people like pretty things, so I can see how the technique could quickly and easily get out of hand. When used correctly though, and when also taking composition into consideration, I don't think there's anything particularly wrong with bokeh. It's also really fun to say. Try it. Bokeh.