The effect is easily obtained with high magnification (as with macro lenses) and large aperature openings. In this case I used a 105mm macro lens set at F2.8, which is the largest aperature I have on this lens. I focused on the tip of one of the tulip buds. It is the tip closest to the camera. The result is that essentially everything but the tip of the bud is out of focus. Nevertheless I find the blur appealing, as the background now seems to be more about color (pink and green complement each other nicely) and less about image detail. Again, your mileage may vary.
This is the best one of about a dozen pictures I took this afternoon.
(Actually, my intention was to fool around a bit with the my Olympus 36R flash, using it for macro shots. It worked perfectly, even when using my old Nikon 105mm lens on a Panasonic camera. The TTL auto feature kept the flash from overpowering the exposure, even at the 12" focusing distance.)
|Panasonic GH2, Nikon 105mm macro, 1/250th, F2.8, ISO 160, Flash in hot shoe at -1EV|