Shooting at wide apertures gives very minimal depth of field at closer distances. Anything not in the plane of focus will be blurred. The wider the apertures, the narrower the depth of field, and the stronger the out-of-focus blur will be. Highlight outlines in this blurry area are popularly referred to as "bokeh".
The closer you get to your subject, the narrower depth of field becomes. If you are shooting close-up macro shots, the depth of field can be a millimeter. You'll get out of focus areas behind your subject even at F16 or F22.
I think "bokeh" (for the most part) is overrated gimmickry. For decades no one really knew or cared what bokeh was, but now people seem to be judging the quality of a lens more for it's bokeh than for more important qualities.
This is the reason that fast lenses have become so expensive in recent years. A fast Nikkor or Canon 55/1.2 lens is bulkier and less sharp than it's slower counterpart, yet these lenses now command very high prices because of the bokeh fad.
I'm not complaining, I'm cashing in on the fad by buying and reselling fast lenses on the big auction site. Adding "great bokeh" to the selling description seems to get an extra 20% in price...
